Method 1 (rooted)
The easiest way you can use RegionLockAway for those on MK2 is to do this:
I did this on the stock MK2 ROM stock.
Since no one either bothered to look in the same forum for the modem thread here is a link to the modems:
1. Root the phone on Stock MK2.
2. Download and install Safestrap.
3. Download MF3 modem.
4. Install the modem using Safestrap from the stock rom slot (what I did)
5. Reboot the phone, go to settings, and confirm you are on the MF3 modem. (this will not affect KNOX or bootloader)
6. Run RegionLockAway 1.3
7. Shut the phone down and insert any other carrier sim and turn the phone on, or leave the sim in after installing the MF3 modem, bypass the code unlock screen and then run RegionLockAway 1.3
8. Reboot and you should see it activate your carrier.
9. You can also flash back to MK2 if you like. (optional)
I can confirm it worked and the T-Mobile sim was accepted. There was no invalid sim prompt or unlock code prompt after doing this. I even flashed back to the MK2 modem and it still stayed unlocked.
Unfortunately the person I got the phone from had reported it stolen and when it went to activate on T-mobile is threw up the MM#6 code meaning the phone can't be activated due to bad IMEI. Apparently the guy who sold it to me assured me it would work on AT&T and everything was good. I had the phone maybe 5 days and after unlocking it later found out he reported it stolen. So yes I got scammed. Luckily I only paid $100 for the AT&T GS4. However for being honest on craigslist that I had a beautiful AT&T GS4 with Bad IMEI I was able to get $250 for the phone from a guy who fixes these problems...and that's all I will say to that. So now I have a Galaxy Note 1.
For those on KitKat 4.4 NB1 Here is more info from DroidDonX
Downgrade from NB1 to MK2, and SIM Unlock SUCESSFUL!!
I got the CSC error too, but to get around that you have to flash the (modem) by flashing the CSC tar in ODIN. You should of got in the MK2 ODIN firmware folder.
It should say this:
Method 2 (posted by muniz_ri)
Alternatively, I337 owners can flash the MDL modem via Odin to re-gain access to the hidden menu(links to signed, odin flashable modems below) then follow the guide in the OP to unlock your phone. Once completed you can re-flash the MK2 modem. I tested this process on my own stock i337 running stock MK2 and it works but follow at your own risk. Also, my knox warranty flag has been tripped for a long time so I don't know if flashing the MDL modem will trip the flag or not. Someone else can chime in on that. Cheers:
MDL Modem: https://mega.co.nz/#!wpUUXQCS!Aws3S1...BTVaEvIzcd3t6M
MK2 Modem: https://mega.co.nz/#!pwESna5I!YK7EKG...9t2EdMK9ofgJKg[/QUOTE]
To finish this method go to this thread:
*muniz_ri has stated he is not sure whether this will trip KNOX or not*
**Method 2 has been confirmed to not trip KNOX by users**
Thanks to RockRatt and deadlysin9 for letting me know it was safe to just flash modems while on MK2 rooted
My method to root the AT&T S4 was saferoot
For those who need to downgrade from 4.4.2 to 4.3
Remember use the CSC slot in Odin
We are downgrading everything but the bootloader when downgrading from 4.4.2 to 4.3
Link for the files needed:
Try this and let me know, BTW this works on SGH-I337 S4 on 4.4.2 Kit Kat w/ stock ROM and NC1 Modem:
1. Download and install the following programs, but do not open them: Regionlock Away v1.3, towelroot v3, BusyBox Free v1.22.1 and Terminal Emulator and Safestrap v3.72. You should also obtain a MF3 modem flash .zip and place it on your internal storage "sdcard" or external storage, just remember where it is. I believe you can have any SIM card that is an unauthorized carrier in your phone at this time. That is of course if you want to unlock your SIM. I personally did not do this but my friend did it and I have read in the XDA forums that you can do this in theory if you so desire.
2. I placed all of the apps mentioned in this post into a single folder for ease of access.
3. Open towelroot and click "make it ra1n."
4. Upon completion, your device should be rooted, no reboot is necessary at this time (takes 5-10 seconds MAX).
5. Your device is now rooted, now download and install SuperSU. Open it and give any program you run from here on out access by clicking "grant" upon opening.
6. Open BusyBox Free v1.22.1 and let it run until complete, I let it complete the smart install but you can click on "install" at the bottom if you want. (don't know if this is required, I just read about it on one of the xda forums or a YouTube video out there somewhere, at any rate, I had heard that you can run it and install everything that needs to be installed and I had heard that you will obtain your overall objective of unlocking your phone. Let an expert elaborate on this one...
7. Download and install Root Checker Basic. Open it and click on "verify root." You should see some text in green that states, "Congratulations! This device has root access!" You just verified you have root
8. Open Terminal Emulator and type "su" (but no quotations "", so just type su), then press enter/return.
9. This should give Terminal Emulator root access via SuperSU. Now type "setenforce 0" (again, without "", so just setenforce 0 and press enter/return).
10. You just allowed your device to open Safestrap without automatically crashing if you didn’t complete step 9. (step 9 must be accomplished every single time you wish to open Safestrap or when ever you seek to boot into Safestrap Mode. I made it a habit to type this in every time I turn on/reboot my device. Let’s hope one of the devs can come up with something to fix this so it is automated and we don’t have to physically type this in every time) *hint* *hint*
11. Now that you opened Safestrap, click on "Install Recovery." If I remember correctly, it will require you to boot upon completion of the installation. Don't remember but if it makes you reboot though, but when you first turn on your phone it will say that Safestrap is disabled and you can either enter "recovery" or "continue." If it does reboot and you get this, just click "continue" to boot normally. At this time, complete step 9 then open Safestrap and click on "reboot to recovery."
Alternate Option 11A. For whatever reason, if you did not reboot your device after clicking "install recovery," upon completion of installing Safestrap, click on "reboot to recovery." You have to click this every time you wish to reboot into Safestrap Recovery Mode. (I could be mistaken but this is the method I use to reboot into recovery each time) Check out my name, I am new to the Galaxy scene.
12. Now that you are in Safestrap, click on "Mount."
13. Mount the storage device you put the MF3 modem on by checking "System" if it is stored on the internal memory (example sdcard\download) or "Micro SDcard" if it is saved to your external Micro SD Card.
14. Back out of that screen and go to main scree in Safestrap.
15. Click on "Install."
16. Click on the actual .zip file for the MF3 Modem Flash file mentioned previously. This will flash your modem from NC1 to MF3.
17. Congrats, you now have an MF3 Modem.
18. Go to main screen in Safestrap. Click on "Reboot," then "System."
I stopped here on my device, but what my friend did on her device, she went on to unlock her SIM in the following steps. I have not done this and I cannot confirm this, maybe someone else can. But from reading threads on XDA, this in theory should work.
Now, for the 19th step, In case you missed the first step to place your unauthorized SIM in your phone, no fear, this is the time when you absolutely have to have it If you wish to unlock your SIM. In theory you can elect to open RegionLock Away and then click on "Region Unlock." I cannot confirm this for I have NOT done this but I have read that your device will reboot or you should reboot at this time. Your device should boot up normally, aside from the screen that says Safestrap is disabled in which you must click on "Continue" to boot normally or wait 10 seconds to boot normally. You should in theory have an unlocked SIM and now have access said network once your device boots up. If it did not work, Re-read this entire 19th step and the 2nd time around you should be good to go.
I hope this worked for you. I cannot confirm anything past the 18th step but in theory it should work for you. Let me know.
I am not responsible if you brick your phone. You should have some working knowledge about your phone as well as rooting and flasing. This is not a comprehensive guide. This is a workaround for those on MK2 firmware where in none of the secret codes to access the SIM lock will work.