General Samsung S21, S21+, and S21 Ultra U1 Firmware (Links)

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renoflightrn

Member
Sep 17, 2012
9
0
Reno
It doesn't allow dual SIM in the US at all. One of the first things I looked for once my AT&T S21 Ultra was unlocked. Even flashing U1 firmware doesn't allow that. However, it does completely convert the phone to the Unlocked version of Samsung's firmware, so your updates won't come with AT&T bloatware, only Samsung apps.
Thank you! Hoping AT&T changes their minds and will turn on dual SIM... seems to just be turned off by the carrier.
 

cjegan2008

Senior Member
May 31, 2008
231
24
Tucson, AZ
I heard it's the carriers turning it off, but haven't seen a solid answer. Samsung still has it on their website that allows dual SIM (using eSIM and a physical SIM) - at least for the ultra.
Idk. You would have to find someone on here who actually has the U1 model and see if they can use eSIM. I doubt the US versions have it. The international models probably do.
 

renoflightrn

Member
Sep 17, 2012
9
0
Reno
It doesn't allow dual SIM in the US at all. One of the first things I looked for once my AT&T S21 Ultra was unlocked. Even flashing U1 firmware doesn't allow that. However, it does completely convert the phone to the Unlocked version of Samsung's firmware, so your updates won't come with AT&T bloatware, only Samsung apps.
One more question - How can you get the bootloader unlocked and go into download mode. No luck with my AT&T version.
 

Geekser

Senior Member
May 18, 2017
1,037
460
Milwaukee
ShimmeringGlass.com
For what it's worth, I flashed the U1 firmware I mentioned with the link a few posts back - but then I also flashed the CSC file from the most recent firmware for G998U - this gives me all the ATT functionality (WIFI calling, Video Calling, etc) without the ATT Bloat. It also includes February Security Update.
 

Quickvic30

Senior Member
Feb 28, 2013
1,411
606
Galaxy
Hello all, it's been a while since I've done some flashing, used to be a flashaholic lol.

So my question is, if I use the HOMCSC will I retain all my data and have the bloat free U1 firmware or must I flash the regular CSC that wipes the phone to make the U1 firmware changes?

AKA I wanna dirty flash U1 over ATT firmware and not lose all my data.

Thanks in advance!
 
Last edited:

mshouman123

Member
Jun 23, 2017
9
0
For what it's worth, I flashed the U1 firmware I mentioned with the link a few posts back - but then I also flashed the CSC file from the most recent firmware for G998U - this gives me all the ATT functionality (WIFI calling, Video Calling, etc) without the ATT Bloat. It also includes February Security Update.
I have an s21 ultra and would like to get att wifi calling mine is unlocked tmobile branded with att sim. Would you be able to let me know what steps/files you flashed to get this ?

Thanks alot !
 

Nettwerk

Senior Member
May 18, 2009
368
51
In Connection
Sorry for disturbing. I have question if I flash from AT&T firmware to XAA U1 firmware via Odin will it change CSC or need to change CSC via Samkey? I know for Exynos models if you flash multi csc firmware then you need Samkey to change CSC to specific one.
 

Geekser

Senior Member
May 18, 2017
1,037
460
Milwaukee
ShimmeringGlass.com
I have an s21 ultra and would like to get att wifi calling mine is unlocked tmobile branded with att sim. Would you be able to let me know what steps/files you flashed to get this ?

Thanks alot !
I didn't follow any special steps. I just flashed it in Odin exactly as I described - I put the G998U1 files for BL, CP and AP into Odin and then added the CSC file from the G998U firmware.

In the meantime, I didn't touch my SIM card like others say they did.

I don't mean to confuse the issue, but Subsequent to all of this, the last time I flashed, I simply flashed the entire firmware file for G998U1 - and on reboot after flashing I still had WiFi calling (the only enhanced calling feature I did not have was ATT Video Calling.
 

cjegan2008

Senior Member
May 31, 2008
231
24
Tucson, AZ
Hello all, it's been a while since I've done some flashing, used to be a flashaholic lol.

So my question is, if I use the HOMCSC will I retain all my data and have the bloat free U1 firmware or must I flash the regular CSC that wipes the phone to make the U1 firmware changes?

AKA I wanna dirty flash U1 over ATT firmware and not lose all my data.

Thanks in advance!
I wouldn't do a dirty flash on this device. The surefire way to remove all the AT&T bloatware is a clean flash.
 

cjegan2008

Senior Member
May 31, 2008
231
24
Tucson, AZ
I have an s21 ultra and would like to get att wifi calling mine is unlocked tmobile branded with att sim. Would you be able to let me know what steps/files you flashed to get this ?

Thanks alot !
You would have to flash this using Odin. I am using the U1 software with AT&T calling working fine, no issues. However, your device has to be on the U1 software without any T-Mobile firmware.
 

cjegan2008

Senior Member
May 31, 2008
231
24
Tucson, AZ
Sorry for disturbing. I have question if I flash from AT&T firmware to XAA U1 firmware via Odin will it change CSC or need to change CSC via Samkey? I know for Exynos models if you flash multi csc firmware then you need Samkey to change CSC to specific one.
CSC will be XAA after flashing this. All updates from then on out will be U1 updates directly from Samsung, no carrier bloat.
 
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moobieboobie

Senior Member
Apr 30, 2011
153
27
I'm waiting on an ATT version to arrive and plan to flash the unbloated firmware here. My question is, once it's flashed, will the phone receive OTA updates via phone or will a new firmware have to be flashed each time? I haven't been on the forums since the S4, so it's been a while... Thanks
 

cjegan2008

Senior Member
May 31, 2008
231
24
Tucson, AZ
I'm waiting on an ATT version to arrive and plan to flash the unbloated firmware here. My question is, once it's flashed, will the phone receive OTA updates via phone or will a new firmware have to be flashed each time? I haven't been on the forums since the S4, so it's been a while... Thanks
It will have the firmware through OTA directly from Samsung, not AT&T.
 
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janeking12

Member
Jan 25, 2021
5
2
I used to adore Samsung S21, S21 +, I was an avid android user, never thought of cheating on it. Until it began to turn off the confidentiality mode of the employee monitoring software (connected to my PC), my geolocation, my ads, and my email distribution. When I switched to an iPhone things got better for some reason, . Do you think i should continue with apple or maybe try upgrade something in the android settings
 

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