# [Guide] Enable AT&T US HD Voice/VoLTE on non-supported W10M phones

#### 73blazer

##### Member
Well, I appreciate your input, I wasn't expecting anything other than ideas.
I thought mabey waiting it might provision itself, I did that yesterday too while the sim was out, waited about 12hrs, nothing. I've downloaded the FFU for the 950 dual sim, but no idea if it's for AT&T or not it was the only north america one in the list, don't have much confidence that will work.

#### 73blazer

##### Member
I really wanted to get my X3 to work. I tryied overlaying any file I thought was modem related from the verizon X3 FFU onto my at&t one, but that bricked the phone (wouldn't boot) until a reflash.

#### 73blazer

##### Member
Well, I got one step closer, mabey. This time I only copied the ADC folders and left modemconfiguration.cab alone. I dunno what modemconfiguration controls, but pre-mod the field test showed all LTE bands active. Does it control more than just what bands show up?
When I reset the phone I got in cellular & sim settings -> apn for lte instead of "not available" I got "nxtgenphone". But system about shows ims registration not registered. So, didn't brick the sims this time, and I got that nxtgenphone thing which I'd never seen before. But still couldn't make a VoLTE call on it.
I did order a single sim RM-1085 but it won't be here for a couple weeks and that's past the cut-off date for at&t shutdown of 3g.

Interestingly enough MMS does seem to work via VoLTE? I know because I have one of the new LTE only microcells at home and when I send an MMS I can watch the traffic light blink.

Hmm...mabey a cigar break will give me my next move.

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#### nate0

##### Senior Member
Well, I got one step closer, mabey. This time I only copied the ADC folders and left modemconfiguration.cab alone. I dunno what modemconfiguration controls, but pre-mod the field test showed all LTE bands active. Does it control more than just what bands show up?
When I reset the phone I got in cellular & sim settings -> apn for lte instead of "not available" I got "nxtgenphone". But system about shows ims registration not registered. So, didn't brick the sims this time, and I got that nxtgenphone thing which I'd never seen before. But still couldn't make a VoLTE call on it.
I did order a single sim RM-1085 but it won't be here for a couple weeks and that's past the cut-off date for at&t shutdown of 3g.

Interestingly enough MMS does seem to work via VoLTE? I know because I have one of the new LTE only microcells at home and when I send an MMS I can watch the traffic light blink.

Hmm...mabey a cigar break will give me my next move.
Yeah the modemconfig cab files alter the QC nvi code which is stored in the more secure QUALCOMM partitions. So for example, all the ims settings are configurable and customized per carrier with hex related format. Stock the RM-1116 does not have the NVI settings stored to register with AT&T properly because that hex format for ims is programmed only if the sw exists on that device to begin with. So, by adding the modem config cabs you allow the phone to alter its own NVI settings. It is possible to use qpst and the nvi editors for Qualcomm but in order to do that on a Lumia we have to be able to authenticate as the nviupdater service to do it, which so far as I know there was nobody able to build an api such as that. On the flip side we can alter any NVI setting file on the X3 or Idol 4s or any other Windows phone that does not use a more secure method like the Lumia's (nviupdater) service.

73blazer

#### 73blazer

yeah I've tried the 950 DS modemconfiguration.cab and while it didn't brick the sims, still no IMS lock. I'll just wait for this new RM-1085 to show up. NIB, $60. And an RM-1105 (single sim 950) with it. nate0 #### nate0 ##### Senior Member yeah I've tried the 950 DS modemconfiguration.cab and while it didn't brick the sims, still no IMS lock. I'll just wait for this new RM-1085 to show up. NIB,$60. And an RM-1105 (single sim 950) with it.
That is a good find/deal cool.

#### 73blazer

##### Member
To Report, I did get this to work on AT&T on a Single Sim 950XL (RM1085), which I've been using for the past several weeks without issue. Everything works, calls, data, sms/mms multi-part txt. I never could get my 950 XL Dual sim (RM1116) to work. Like you said it does also required a Lumia 950 IMEI to be registered with AT&T as your device.

I compared nate0's posted files with the Single Sim 950 ATT Branded device i got as well (RM1105) and they were all the same, so no updates in later builds from your original post.

I did find some more WiFi-C files on the RM-1085 device which came from Europe. Coupled with the registry keys for wifi-c The settings finally showed up in the sim settings menu, but it does not seem to function. I really wonder what would happen if I registered an IMEI from an iPhone or something that has both VoLTE and WiFi-C "enabled" from AT&T's end.... if that would make it all work or if using an IMEI from a different platform will make all of it not work. I dunno. May be worth a shot.

Anyway, I'm happy with the 950XL working post-3g shutdown on AT&T's network thanks to nate0's detailed instructions in this post, thanks nate0! Wi-FI-C would be icing on the cake. I may continue to dig around and experiment.

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nate0

#### maximum56

##### Member
Hello!

New to the forum and was looking to get a single sim 950 xl working on one of the ATT carriers (Puretalk).

Is this a big lift to get it done? Trying to read through everything and see if it is reasonable for me.

Thanks for the Help!

#### 73blazer

##### Member
Well, that depends on your experience and comfort level with breaking into your phone and copying some files. It helps to have some knowledge of windows development and how things work so you know what to do and what to expect when your doing certain things or if something is going wrong.
I can write up all the steps you need to take and give the exact versions and download for the vcreg/interop that works on the 950xl but if your not comfortable or don't know how to use certain tools like sftp and whatnot, then it may be a long road for you.

#### gchq

##### Member
To Report, I did get this to work on AT&T on a Single Sim 950XL (RM1085), which I've been using for the past several weeks without issue. Everything works, calls, data, sms/mms multi-part txt. I never could get my 950 XL Dual sim (RM1116) to work. Like you said it does also required a Lumia 950 IMEI to be registered with AT&T as your device.

I compared nate0's posted files with the Single Sim 950 ATT Branded device i got as well (RM1105) and they were all the same, so no updates in later builds from your original post.

I did find some more WiFi-C files on the RM-1085 device which came from Europe. Coupled with the registry keys for wifi-c The settings finally showed up in the sim settings menu, but it does not seem to function. I really wonder what would happen if I registered an IMEI from an iPhone or something that has both VoLTE and WiFi-C "enabled" from AT&T's end.... if that would make it all work or if using an IMEI from a different platform will make all of it not work. I dunno. May be worth a shot.

Anyway, I'm happy with the 950XL working post-3g shutdown on AT&T's network thanks to nate0's detailed instructions in this post, thanks nate0! Wi-FI-C would be icing on the cake. I may continue to dig around and experiment.

Just for some clarification - are you saying that you got the single SIM XL working without a branded AT&T 950 IMEI? I have a dual SIM 950XL - it sailed through the 3G shutdown but a couple of weeks ago incoming calls go direct to voicemail and outgoing are intermittent, sometimes call dropped, sometimes work but always take a long time to connect and ring. Everything else works, text, Visual Voicemail.

Edit - I have just ordered an unbootable AT&T 950 from Ebay. It should be here in a week and then I think I can get the IMEI number from the cover where the SIM is inserted? From what I have read the next step is to contact customer service (Chat so that they can copy and paste numbers) and ask them to replace the existing IMEI with the one from the unbootable device?

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#### 73blazer

##### Member
I got an unbranded 950XL single sim (Rm1085) to work WITH a at&t branded 950 IMEI registered with them.
Without the 950 imei registered with them, it did not work.
I was not able to get the dual sim 950xl to work.
The 22feb was only a start date of the shutdown, alot of areas have gone off, but some are still on but slowly, they will all go away. I know my area did a couple weeks ago as in the ##3282# field test app which shows LTE/4g and 3g frequencies I used to see 3g frequencies still being recieved, now I do not. All the 3g ones are all dead.

#### gchq

##### Member
I got an unbranded 950XL single sim (Rm1085) to work WITH a at&t branded 950 IMEI registered with them.
Without the 950 imei registered with them, it did not work.
I was not able to get the dual sim 950xl to work.
The 22feb was only a start date of the shutdown, alot of areas have gone off, but some are still on but slowly, they will all go away. I know my area did as in the ##3282# field test app which shows LTE and 3g frequencies I used to see 3g frequencies still being recieved, now I do not. All the 3g ones are all dead.
I just added an edit to my original post as you were posting this - thanks for you fast response. If I have to I will get a single SIM XL, rather than downgrade to crappy Android or the even worse iThing.

Once I get the throw-away I, Arnie style, will be back for some more hand holding - my area is Windows desktop dev and servers, so it will be the first time playing with phone OS. I have just downloaded Interop Tools onto the phone from the store.

Current XL is RM-1116_15357

#### 73blazer

##### Member
I've found the store version doesn't work. I think the last store version wasn't on the latest version of the mobile 10 and when your running that, the store interop no longer worked.
I have a whole writeup on how to do it all on the 950xl. you need specific versions of vcreg and interop, and a back version visual studio on a desktop/laptop that has the iutool still in it. I'll post the write up tomorrow sometime , it was rather my notes and needs cleaned up for forum consumption.

nate0

#### gchq

##### Member
I've found the store version doesn't work. I think the last store version wasn't on the latest version of the mobile 10 and when your running that, the store interop no longer worked.
I have a whole writeup on how to do it all on the 950xl. you need specific versions of vcreg and interop, and a back version visual studio on a desktop/laptop that has the iutool still in it. I'll post the write up tomorrow sometime , it was rather my notes and needs cleaned up for forum consumption.
'Back Version' of VS? I have 2017, 2019 and 2022 on my current machine and some older versions on Server 2016 (2008, 2010, 2012, 2013, 2015) that I use as a workstation and connections to servers using internal IP. Some older versions of VS are flakey and some don't like to run because they got confused with the developer subscription settings. I've not fully installed Interop yet, but the preamble gives the impression it is a 2021 version (the older versions ended up in 'Extras' whereas this is not.) I look forward to reading your polished notes

Thanks again for your prompt replies.

Oh - one other question. Why does the 950 work, and is on the 'approved' list for AT&T, but the 950XL does not. As far as I am aware the only difference is a larger processor, more RAM and a larger screen but the telecoms hardware is the same? Nobody at AT&T seems to be able to answer that question, and curious minds 'n' all that...

Edit - Interop version is showing as 2.1.29.0 running on 10.0.15254.603

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#### maximum56

##### Member
I purchased a 950XL Single Sim version and it worked right away with the Puretalk SIM.

The only downside is that the version of windows 10 on the phone is very old and the windows update feature of the phone doesn't work. The store doesn't even work.

I thought that if I log in after a phone reset it would pull everything over?

I have a dual sim using the same windows account I was hoping to move everything over.

2. Is there a way to transfer all the apps from the dual sim to the single sim?

Thanks!

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#### gchq

##### Member
'Back Version' of VS? I have 2017, 2019 and 2022 on my current machine and some older versions on Server 2016 (2008, 2010, 2012, 2013, 2015) that I use as a workstation and connections to servers using internal IP. Some older versions of VS are flakey and some don't like to run because they got confused with the developer subscription settings. I've not fully installed Interop yet, but the preamble gives the impression it is a 2021 version (the older versions ended up in 'Extras' whereas this is not.) I look forward to reading your polished notes

Thanks again for your prompt replies.

Oh - one other question. Why does the 950 work, and is on the 'approved' list for AT&T, but the 950XL does not. As far as I am aware the only difference is a larger processor, more RAM and a larger screen but the telecoms hardware is the same? Nobody at AT&T seems to be able to answer that question, and curious minds 'n' all that...

Edit - Interop version is showing as 2.1.29.0 running on 10.0.15254.603
I got the AT&T 950 and they have swapped out the IEME. What is the next stage?

Incidentally - the SIM has always registered as 'LTE' but I was curious what would happen if I changed it from Automatic. Selecting AT&T(LTE), either one, just drops the connection but I am curious as to what AT&T Forbidden is all about?

#### gchq

##### Member
Has everyone in this thread emigrated? Piled up gold in the back of an SUV and headed for the hills? It's been very quiet for a while!

I have another question. Setting quiet hours and a breakthrough list used to be via Cortana which, I think, was the most annoying thing MS ever came out with. Accidently hit the button and 'I can help you if...' woke everyone up for a three-mile radius, so not sorry to see that go. Thankfully the list persisted after it was dropped, but I have no idea how to edit it or add any more breakthrough numbers, which brings me back to how I got to this.

A hard reset could cause some issues with existing settings. I thought of getting another phone, single SIM XL, get that working with AT&T and manually move everything over, and then it dawned on me that quiet hours and the breakthrough list could be an issue.

Has anyone else found a workaround?

#### 73blazer

##### Member
SO here's how to make any x50 phone work for AT&T post 3g (you don't need visual studio after all, the driver kit will install without it and give you the iutool you need from it):

NOTE: This only works for single sim x50 devices and you must register a at&t branded Lumia 950 (RM-1105) IMEI with AT&T for this to work. Some steps are order dependent so follow them closely. I've found other versions of iterop and vcreg to not work so use the versions I put here
1. Update your phone to the latest windows 10 mobile version from the settings->phone update. You should eventually get to 10.0.15254.603
2. Turn on developer mode on the phone settings
3. Unpack the Inteerop ZIP from this post on your PC
4. Plug your phone to the PC via USB
5. in your PC filnd your phone in files explorer and On the phone's (not sd card) download folder make a folder called interop and another called vcreg
6. COpy the interop.xappbundle and the dependency folder to the phones downloads/interop directory
7. on PC Unpack the vcreg zip from this post
8. Copy the vcreg .xappbundle and dependency folder to the phones download/vcreg folder
9. on PC unpack the ndtk_acer_services zip
10. Copy the two dll's from the acer zip to the phones documents folder (not the .spkg file)
11. On the phone goto file explorer Install interop dependencies from the downloads folder (just pick them with your finger) (wait about 10s between each one, they won’t tell you they’re installing or when they’re finished, if you pick too quickly and one is still installing the others won’t)
12. On the phone install the main interop app
13. On the phone install the VCREG dependencies
14. On the phone install the vcreg main app
15. At this point after about 1-2mins you should see interop and vc reg in your applications list on the phone.
16. On your PC install windows driver kit (this has the iutool you will need) . You need a version that is close or below the phone, the current versions since they removed mobile from them don’t have the iutool,so you need a back level version. available at Windows Build: 10.0.15063 at https://networchestration.wordpress.com/2017/12/10/wdk-download/ (the actual download comes from Microsoft, the page is just a collection of links to the back versions MS doesn’t advertise anymore). Use the EXE under Windows Build: 10.0.15063
17. On phone, open vcreg app and on the bottom bar go for x50 unlock, step 1 (it will present a acer services not running error, that is ok)
18. The VCREg package you unpacked on the PC has a .spkg file in it. This is a devel service you need installed on the phone in order to unlock it. With your phone connected via USB (and the only phone connected to the PC) open a command shell on the PC as administrator and cd to the directory where iutool located in C:\Program Files (x86)\Windows Kits\10\Tools\bin\i386 installed with the the driver kit above. Then run ‘iutool –V –p “C:\path\to\acerspkgdir”’ just the directory path not the spkg itself. It will find any spkg in that dir and install it on the phone. You should see the iutool go thru some steps and pause then your phone will reboot to the gears and then reboot again. when it reboots again iutool in your command shell should complete and say one package installed successfully.
19. On phone go back to vcreg app->unlock x50->step 2
20. reboot phone
21. on phone go back to vcreg app->unlock x50->step 3
22. reboot phone
23. on phone go back to vcreg app->unlock x50->check live interop/capability unlock
24. Now open interop app->no auth->choose this device (this part takes about 15s for some reason?) and goto hamburger menu->ssh account manager you should see two users. If you don't, you didn't do the vcreg unlock part right. Your going to add a third user called "System". Once highlight your new System user and pick the templates for selected tab on top and hit "apply full sftp access" , then go to options tab and change auth method to password, leave username as LocalSystem and type in a 4 digit pin (do not use letters or longer than 4 numbers). Sometimes this password doesn't stick, keep highlighting the system user, goto options tab if your password doesn't have 4 dots it didn't stick, type it in again and go out and back in until the 4 dots stick
25. Now on PC you can install filezilla (google it for download or use any SFTP client). Open filezilla and type in your phones IP address and choose sftp user System password whatever 4 digit pin you used...and connect. It should connect and see the full windows C: directory on your phone.
26. Do the MO_VoLTE copy to your phobe as outlined the very first post in this thread. Then follow the "For 950/xl) directions in the very 1st post in this thread. Except hard reset is not required only reboot. After you copy the modem files after some time (a few mins) your phone should pop up a box that says sim settings have changed, please reboot. Reboot.
27. Now in settings->cellular and sim->sim settings and turn on "Enhanced 4g LTE services"

#### Attachments

• VCREG1.7+dependencies.zip
15.9 MB · Views: 13
• Interop Tools 1.9-RC3 [Winphone Iz].zip
13.9 MB · Views: 12
• ndtk_acer_services.zip
398.3 KB · Views: 13
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#### gchq

##### Member
SO here's how to make any x50 phone work for AT&T post 3g (you don't need visual studio after all, the driver kit will install without it and give you the iutool you need from it):

NOTE: This only works for single sim x50 devices and you must register a at&t branded Lumia 950 (RM-1105) IMEI with AT&T for this to work. Some steps are order dependent so follow them closely. I've found other versions of iterop and vcreg to not work so use the versions I put here
1. Update your phone to the latest windows 10 mobile version from the settings->phone update. You should eventually get to 10.0.15254.603
2. Turn on developer mode on the phone settings
3. Unpack the Inteerop ZIP from this post on your PC
4. Plug your phone to the PC via USB
5. in your PC filnd your phone in files explorer and On the phone's (not sd card) download folder make a folder called interop and another called vcreg
6. COpy the interop.xappbundle and the dependency folder to the phones downloads/interop directory
7. on PC Unpack the vcreg zip from this post
8. Copy the vcreg .xappbundle and dependency folder to the phones download/vcreg folder
9. on PC unpack the ndtk_acer_services zip
10. Copy the two dll's from the acer zip to the phones documents folder (not the .spkg file)
11. On the phone goto file explorer Install interop dependencies from the downloads folder (just pick them with your finger) (wait about 10s between each one, they won’t tell you they’re installing or when they’re finished, if you pick too quickly and one is still installing the others won’t)
12. On the phone install the main interop app
13. On the phone install the VCREG dependencies
14. On the phone install the vcreg main app
15. At this point after about 1-2mins you should see interop and vc reg in your applications list on the phone.
16. On your PC install windows driver kit (this has the iutool you will need) . You need a version that is close or below the phone, the current versions since they removed mobile from them don’t have the iutool,so you need a back level version. available at Windows Build: 10.0.15063 at https://networchestration.wordpress.com/2017/12/10/wdk-download/ (the actual download comes from Microsoft, the page is just a collection of links to the back versions MS doesn’t advertise anymore)
17. On phone, open vcreg app and on the bottom bar go for x50 unlock, step 1 (it will present a acer services not running error, that is ok)
18. The VCREg package you unpacked on the PC has a .spkg file in it. This is a devel service you need installed on the phone in order to unlock it. With your phone connected via USB (and the only phone connected to the PC) open a command shell on the PC as administrator and cd to the directory where iutool located in C:\Program Files (x86)\Windows Kits\10\Tools\bin\i386 installed with the the driver kit above. Then run ‘iutool –V –p “C:\path\to\acerspkgdir”’ just the directory path not the spkg itself. It will find any spkg in that dir and install it on the phone. You should see the iutool go thru some steps and pause then your phone will reboot to the gears and then reboot again. when it reboots again iutool in your command shell should complete and say one package installed successfully.
19. On phone go back to vcreg app->unlock x50->step 2
20. reboot phone
21. on phone go back to vcreg app->unlock x50->step 3
22. reboot phone
23. on phone go back to vcreg app->unlock x50->check live interop/capability unlock
24. Now open interop app->no auth->choose this device (this part takes about 15s for some reason?) and goto hamburger menu->ssh account manager you should see two users. If you don't, you didn't do the vcreg unlock part right. Your going to add a third user called "System". Once highlight your new System user and pick the templates for selected tab on top and hit "apply full sftp access" , then go to options tab and change auth method to password, leave username as LocalSystem and type in a 4 digit pin (do not use letters or longer than 4 numbers). Sometimes this password doesn't stick, keep highlighting the system user, goto options tab if your password doesn't have 4 dots it didn't stick, type it in again and go out and back in until the 4 dots stick
25. Now on PC you can install filezilla (google it for download or use any SFTP client). Open filezilla and type in your phones IP address and choose sftp user System password whatever 4 digit pin you used...and connect. It should connect and see the full windows C: directory on your phone.
26. Now follow the "For 950/xl) directions in the very 1st post in this thread. Except hard reset is not required. After you copy the modem files after some time your phone should pop up a box that says sim settings have changed, please reboot. Reboot.
27. Now in settings->cellular and sim->sim settings and turn on "Enhanced 4g LTE services"

Thank you for that.

Is there a reason that the dual SIM (the one I use on a daily basis) not supported? The original post in this thread used a dual SIM.

Is there a workaround for quiet hours and the breakthrough list? It would then be the perfect phone.

Getting totally away from this subject, but on the 'I can sure pick 'em' list of phones that have been dropped, I also have an Essential PH1. Is there a thread here that details how to update Android now that Essential have packed their bags and left the room?

#### 73blazer

##### Member
Thank you for that.

Is there a reason that the dual SIM (the one I use on a daily basis) not supported? The original post in this thread used a dual SIM.

Is there a workaround for quiet hours and the breakthrough list? It would then be the perfect phone.

Getting totally away from this subject, but on the 'I can sure pick 'em' list of phones that have been dropped, I also have an Essential PH1. Is there a thread here that details how to update Android now that Essential have packed their bags and left the room?
It does say that, but, doesn't work. I tried it and it bricks the cellular modem and I had to reload a rom from PC to get it back. The modem files for dual sim are completely different than for single sim, there is probably a way to unpack the cab's in there and merge the single sim ones into the dual sim format but it's much easier to just get a single sim device. The dual sim stuff just really complicates things.
The only reason a single sim 950 works is because AT&T sold it in their store and had the right rom to work on their network with the VoLTE/HD Voice stuff. So...that is where the modem files came from and can be used on any phone with the same modem (x50 devices in theory).... I tried on a X3 and that phone is laid out all different, the modem files aren't even in the same directory. The modem is different so they likely wouldn't work anyway..etc..etc..
I've no idea on your Android question, never touched the stuff. To me using Android or iOS would be the same as using coke.

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This is how I enabled AT&T US HD Voice/VoLTE on the Lumia 950 XL Dual sim and the factory Unlocked Alcatel IDOL 4s. It should work on the Lumia 950 Dual sim too, but I have not tested this method on it yet.

*Requires full file system access with MTP or SFTP using Interop tools
*All the files attached were taken from the latest AT&T Lumia 950 FFU (01078.00053.16236.35035 - OS 10.0.10586.318)
*To reset everything back to original factory settings requires either a re-flash or you can take the files you backed up before hand and replace them back.
**The one caveat to this is you need to use an AT&T Lumia 950 imei to register to your ICCID (sim card ID) with AT&T customer support to enable the hd voice/ims registration to come online. It might work with a Lumia 830 imei for AT&T too.
***There was mention of AT&T possibly whitelisting your device. This would allow IMS provisioning to complete without the need to have AT&T update your IMEI with that of a AT&T branded one. Seems even though you can ask AT&T to do this, it has not actually been proven to work. The only for sure way is to use a AT& branded Lumia 950 IMEI.

Update 7/20/2017: Updated files attached to include the specific ATT-US files from the 950 XL rom RM-1085_15919 (product: 059X7S5). The modem file is slightly different as it provisions with the same bands that come default already on the 950XL, it will not remove band 17 like the 950 ATT modemconfiguration.cab file does. The modem files as far as I know only work on the x50 Lumia models and not OEM models.

Install Interop Tools
- Here is the link. I used version InteropTools_1.9.437.0_arm_RC3.

Install Swish
- This sftp client found here (needed for Lumia 950/XL) for explorer sftp support. For the IDOL 4s enable Full file system access via MTP with read write access in Interop Tools under the Unlock options/settings.

- In Interop Tools go the SSH--Account Manager and add an account. The account user name should be System.

- Tap the account System so it is highlighted and then tap templates to use.

- Tap enable full file system access with sftp. Then go to the template options and hit the authentication drop down setting it to password.

- Once your phone is on wifi, add an SFTP Connection under Swish. Set the user to system. Set the path to /c/. Once added double click it and login with the pin you set. Explorer will open with your phones files. There is a guide in more detail on sftp file system access made by snickler if you need to see more details about this method.

For the Lumia 950/XL do the below:

- Then Copy and replace the files under C:\Programs\CommonFiles\ADC\Microsoft and C:\Programs\CommonFiles\ADC\OEM with the files of the zip file titled ADC.zip

- Copy and backup the file under C:\Programs\CommonFiles\OEM\Public\MMO\Multivariant.

- Then Copy and replace the file under C:\Programs\CommonFiles\OEM\Public\MMO\Multivariant with the contents of the zip file titled modemconfiguration.zip

- From there do a hard reset.

For the Alcatel IDOL 4s do the below using full file system access with MTP:

- Then Copy and replace the files under C:\Programs\CommonFiles\ADC\Microsoft and C:\Programs\CommonFiles\ADC\OEM with the contents of the zip file titled ADC.zip

- From there do a hard reset.

When the OOBE setup returns after hard reset, you may have a light blue/cyan theme and the display/dpi/font size may be a bit different too. This is due to the packages used from the AT&T 950. Go through the normal setup and let it fully boot to the start screen. Wait for the prompt to tell you to reboot your phone for settings/sim card settings to change/update.

Alternatively you can add the two files in the zip file titled MO_VoLTE_1117.zip to the c:\windows\system32. This will replace the MO_VoLTE_Label_1117.dll and MO_VoLTE_Description_1117.dll details found near the volte toggle under Sim settings with the proper descriptions.

To reset everything back to original factory settings requires either a re-flash or you can take the files you backed up prior and replace them back.

Thanks to the creator of interop tools @gus33000. Without access to that tool/app this and other things like this would not be possible. To @snickler for finding and explaining the sftp file system access in a guide to help others like me use that method.
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This is how I enabled AT&T US HD Voice/VoLTE on the Lumia 950 XL Dual sim and the factory Unlocked Alcatel IDOL 4s. It should work on the Lumia 950 Dual sim too, but I have not tested this method on it yet.

*Requires full file system access with MTP or SFTP using Interop tools
*All the files attached were taken from the latest AT&T Lumia 950 FFU (01078.00053.16236.35035 - OS 10.0.10586.318)
*To reset everything back to original factory settings requires either a re-flash or you can take the files you backed up before hand and replace them back.
**The one caveat to this is you need to use an AT&T Lumia 950 imei to register to your ICCID (sim card ID) with AT&T customer support to enable the hd voice/ims registration to come online. It may work with lets say a Lumia 830 imei for AT&T too. I do not have one anymore to test though.

Update 7/20/2017: Updated files attached to include the specific ATT-US files from the 950 XL rom RM-1085_15919 (product: 059X7S5). The modem file is slightly different as it provisions with the same bands that come default already on the 950XL, it will not remove band 17 like the 950 ATT modemconfiguration.cab file does. The modem files as far as I know only work on the x50 Lumia models and not OEM models.

Install Interop Tools
- Here is the link. I used version InteropTools_1.9.437.0_arm_RC3.

Install Swish
- This sftp client found here (needed for Lumia 950/XL) for explorer sftp support. For the IDOL 4s enable Full file system access via MTP with read write access in Interop Tools under the Unlock options/settings.

- In Interop Tools go the SSH--Account Manager and add an account. The account user name should be System.

- Tap the account System so it is highlighted and then tap templates to use.

- Tap enable full file system access with sftp. Then go to the template options and hit the authentication drop down setting it to password.

- Once your phone is on wifi, add an SFTP Connection under Swish. Set the user to system. Set the path to /c/. Once added double click it and login with the pin you set. Explorer will open with your phones files. There is a guide in more detail on sftp file system access made by snickler if you need to see more details about this method.

For the Lumia 950/XL do the below:

- Then Copy and replace the files under C:\Programs\CommonFiles\ADC\Microsoft and C:\Programs\CommonFiles\ADC\OEM with the files of the zip file titled ADC.zip

- Copy and backup the file under C:\Programs\CommonFiles\OEM\Public\MMO\Multivariant.

- Then Copy and replace the file under C:\Programs\CommonFiles\OEM\Public\MMO\Multivariant with the contents of the zip file titled modemconfiguration.zip

- From there do a hard reset.

For the Alcatel IDOL 4s do the below using full file system access with MTP:

- Then Copy and replace the files under C:\Programs\CommonFiles\ADC\Microsoft and C:\Programs\CommonFiles\ADC\OEM with the contents of the zip file titled ADC.zip

- From there do a hard reset.

When the OOBE setup returns after hard reset, you may have a light blue/cyan theme and the display/dpi/font size may be a bit different too. This is due to the packages used from the AT&T 950. Go through the normal setup and let it fully boot to the start screen. Wait for the prompt to tell you to reboot your phone for settings/sim card settings to change/update.

Alternatively you can add the two files in the zip file titled MO_VoLTE_1117.zip to the c:\windows\system32. This will replace the MO_VoLTE_Label_1117.dll and MO_VoLTE_Description_1117.dll details found near the volte toggle under Sim settings with the proper descriptions.

To reset everything back to original factory settings requires either a re-flash or you can take the files you backed up prior and replace them back.

Thanks to the creator of interop tools @gus33000. Without access to that tool/app this and other things like this would not be possible. To @snickler for finding and explaining the sftp file system access in a guide to help others like me use that method.
It worked on my Lumia 950 XL
Look on LumiaFirmware.com for an FFU from your provider (in my case the Lumia 950) mount it with ImgMount and extract the files mentioned above.
for me no reset was necessary, as soon as I pasted the files in the ADC folder I got a message that "SIM settings have been changed please restart" and IMS registration was on
That's my findings so far
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I want to enable it for "Jio" a carrier in INDIA that provides VoLTE services but only android and ios users are able to use it and they donot sell a specific lumia with VoLTE services or there carrier name on it.
*I am using L950XL DS Indian Variant.
*Is this possible??? If yes can you guide me how to edit configuration files to do this.
I was mainly referring to US carriers. You would need to get a hold of a Windows 10 Mobile handset that supports VoLTE on Jio and build new nvi file entries for the Lumia. I don't know of a model that would support Jio VoLTE except maybe the IDOL 4s Pro model that support European Countries. Once you find a Windows 10 Mobile phone that supports VoLTE on that carrier you a starting point.
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@spe317
Since you are reflashing anyway...once you verify all the files are in place. Do full_nvi_update not factory_reset.

thor2.exe -mode uefiflash -ffufile <ffufile_RM-xxxx.ffu> -do_full_nvi_update -skip_flash -reboot

This leaves the modem alone as a single sim, and only reintializes the NVI settings with an update from the nvi files.
If still having an issue you can try a hard reset too. I am not certain why your sim would be doing this...Are you using the Lumia 950 modemconfiguraton.cab file from my first post or are you using the 950 XL files I attached (File Type: zip 950XL_RM-1085_15919_ATT-US_files.zip)
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I had that happen once to an AT&T sim. Except it was not as obvious as yours...my issue was that it would just not lock LTE bands. Took me a week to realize it was due to a bad sim. Glad you caught it quick.

Just confirmed with ATT and received an IMS lock. Provisioned my phone unbranded 950xl DS. Thanks!