yashsingh1/xdaforums huggingface dataset:
[Samsung Galaxy S21 Ultra] kmdigital:
I bought an unlocked S21 Ultra last fall that was originally sold by T-Mobile, and I initially used it with H2o (AT&T) and it always worked fine, though it never got 5g service, though I'm not sure that 5g has been implemented yet by AT&T in the Phoenix market, at least not the C-band

On Jan 21, it automatically updated the software so that it now shows SM-G998U_OYN_ATT_12_0018 ATT/XAA,TMB/TMB as the Service provider software version, so it seemingly has both AT&T and T-Mobile software at this time. At that time, it also switched from showing the T-Mobile logo on bootup to showing the AT&T logo, and I think it added, NR B66 as an additional radio band (in addition to NR B41, B71 and the UW bands of B260 and B261). Earlier this week I switched to Visible and while it works fine on 4g LTE, I'm not getting any 5g connectivity. In researching bands, the only one that I have that Verizon uses is the NR B66, while I probably really need NR B2, B5 and in particular B77 to get the new C-band.

The question is, will the phone at some point automatically update to VZW software, and at that point enable additional bands that I need to get 5g? Or is there a way of forcing this? Or what is the best option to enable 5g on this phone? I really don't want to switch to the U1 software as that seems to require a factory reset, and I'm not keen on going through reconfiguring everything again and getting all my icons back where I want them.

Or will this phone not support these bands unless the U1 software is first installed?

Thanks!
[Samsung Galaxy S21 Ultra] kmdigital:
Anyone?
[Samsung Galaxy S21 Ultra] RedWave31:
Have you tried switching to a Verizon compatible firmware?

With ODIN, you can switch firmwares without losing data.

I suggest trying that, US carrier optimization is known to be the worst
[Samsung Galaxy S21 Ultra] kmdigital:
No, I have not tried that. Sorry to ask a dumb question, but what firmware should I use, and where do I find it? I ask because the "official" firmware seems to be from Jan 2021, and it seems to be the U1 option, not carrier specific firmware. I've done some searching, but I haven't been able to find the Verizon version so far. Thanks.
[Samsung Galaxy S21 Ultra] RedWave31:
I'm on an European 21U, for the USA version, you need to check this guide

https://xdaforums.com/t/g998u-and-g998u1-firmware-links-and-flashing-discussion-here.4220111/unread
[Samsung Galaxy S21 Ultra] RedWave31:
I think you need to go from U1 to U (VZW) to see if that solves it.

Can't help on anything else, since on Exynos (European) devices, flashing is much easier than on Snapdragon devices.
[Samsung Galaxy S21 Ultra] kmdigital:
I read the link above in detail, and it says that the only difference in the 5 files is the "USERDATA", otherwise the other 4 files are identical between vendors. So USERDATA seems to be a critical file in regards to switching from T-Mobile to Verizon. My concern is that further down in the first article it says that flashing the USERDATA file will wipe the existing data.

- HOME CSC file keeps data intact; using the other CSC will wipe data. Flashing USERDATA will also wipe data.

If this is true, and the only way to manually get the VZW info that I'm looking for without flashing to U1, there doesn't seem to be any advantage to flashing this using Odin, as it'll also wipe my user data. In other words, if I go that route, I'd be better off just flashing to U1, and try that. Theoretically, this should give me everything that I need without first flashing to VZW, and if it'll work with Verizon/Visible without the VZW bloatware, then that would definitely be preferred.

My entire reason for trying all this is to try to get the additional NR radio bands, specifically N2, N5 and N77, which I don't have with the T-Mobile software.

As for backing up the phone and then restoring it, does Odin provide this capability? Or is Samsung Kies a much better option? The Kies software seems to be made for this, so if this is the case and it'll exactly restore the phone like it was before, then it wouldn't actually be a big deal to backup, flash and then restore the phone.
[Samsung Galaxy S21 Ultra] MidtownHD:
it's a problem with the T-Mobile S21 series, you need to flash U1 software.
[Samsung Galaxy S21 Ultra] kmdigital:
Not really what I wanted to hear, but sounds like you have experience with this. I take it that the factory T-.Mobile software (or is it firmware?) essentially locks out the NR bands that they don't have, even if other software is installed on top of it. Thx
[Samsung Galaxy S21 Ultra] Ptuk:
As a UK user of Snapdragon that's very interesting that you get n78 c band. I am on

the G998w version and here is my dialler code *#2263# result. As you can see it has no n78 which is important in the UK. Could I see your result just to check all the bands?
[Samsung Galaxy S21 Ultra] kmdigital:
Here you go. As you can see I have both N77 and N78 bands. What I find interesting is that it says Sim 1 is ATT, which isn't what I'm using.

Here you go. What's interesting is that it says Sim 1 is ATT, which isn't what I'm using.
[Samsung Galaxy S21 Ultra] Ptuk:
Thank you. Yes weird the att thing. I think I will give it a crack to move to u1. Seems that the differentiation between exynos and snapdragon has fallen and that channels are no longer an impediment to using snapdragon in Europe. I also got ota update of my w phone in UK which I wasn't sure would happen.
[Samsung Galaxy S21 Ultra] kmdigital:
Yeah, I see that you don't have any C-bands, plus you have the TMB N41 and N71 bands, which is very similar to what I had prior to the U1 flash, but lost for some reason with U1, possibly because it seems to think that it's ATT for some reason. I'd be very interested in knowing what bands you have after a U1 flash.
[Samsung Galaxy S21 Ultra] Ptuk:
I'll tell you as soon as I've got the nerve to do another flash!
[Samsung Galaxy S21 Ultra] mapl.ph:
@Ptuk and @kmdigital , will follow your conversation as I'm needing the N78 5g band. I flashed G998W last night but no luck. Weird is that I was from U then U1 but did not have get to see the N78 band appear.

@kmdigital , can you point me out on which firmware you have installed so I can try and how you actually flashed it. Thanks. Badly needing n78.
[Samsung Galaxy S21 Ultra] Ptuk:
Sorry to clarify....you flashed from G998w to u then u1? If so can you tell me which u1 you used...I'm wondering whether kmdigitals success is Verizon related or not
[Samsung Galaxy S21 Ultra] mapl.ph:
I was originally on G998U then flashed to G998U1 and nothing was changed. Hoping using an universal U1 firmware I would get the N78 band but no luck.

Then, last night I flashed to G998W and lost 260 and 261. Same result no n78 band. I would like to know how @kmdigital was able to get the N78 which I badly need. On download mode my s21 ultra shows ATT at the upper part.

From G998U1UES5BVC1 to G998WVLS5BVAB. I cant recall which G998U I had prior to U1
[Samsung Galaxy S21 Ultra] kmdigital:
Yes, I downloaded it from SamFw.com, file name Samfw.com_SM-G998U1_XAA_G998U1UES5BVC1_fac
[Samsung Galaxy S21 Ultra] yygemmi770:
When on U1 firmware, the device will restart upon a SIM card being inserted and load the bands needed for that provider. However, I have seen with certain MVNO's it doesn't act the same as a major Carrier when on U1, meaning that it will not register properly (why it still shows ATT for csc and not VZW). It seems that the csc is ATT because it doesn't register your SIM as VZW. Try to find a VZW SIM (doesn't need service) and allow the restart, then put back in your Visible SIM. My guess is the phone will not ask for a restart and will have the Verizon bands loaded from the restart when you inserted the VZW SIM.
[Samsung Galaxy S21 Ultra] kmdigital:
I'll see what I can come up with. However, I am currently showing all the Verizon bands (except N261, which I don't care about), so I'm not sure how that would necessarily be beneficial. Would/should there be any benefit to having VZW CSC vs ATT? If this is updated, that would seem to be the primary difference, though I don't know if having it actually makes any operational difference.

Thx
[Samsung Galaxy S21 Ultra] mapl.ph:
Are you using eSim or physical SIM?
[Samsung Galaxy S21 Ultra] kmdigital:
Physical SIM, since Visible only supports eSim on Apple and a few Pixel devices at this time.
[Samsung Galaxy S21 Ultra] yygemmi770:
There is a difference in the sense that you are using VZW service, but your phone thinks it's ATT. I am sure that having the proper CSC would give you optimal performance. I am curious if WIFI calling is working correctly for you. If it is working for you now then that is great. Just pointing out what I see etc.
[Samsung Galaxy S21 Ultra] kmdigital:
Good point, and while it seems to be working well, optimization is always a good thing.

As for Wi-Fi calling, I just tried it and now I have to use Samsung Band Selector app (available in the Play Store) to get to this setting, which is odd since it was in the main Mobile Networks setting previously. I can enable it, and assume that it would work, but I don't like it, so I always just keep it off. I would use it if it were the only option, such as being in an area w/o a cellular signal, but otherwise, my experience is that Wi-Fi calling tends to be a bit glitchy. I should note that while this option was previously in the main settings menu, I couldn't enable it there when on H2o, but I could enable it with the band selector app. I also had to disable it via the app once it was enabled. Interestingly, when I switched to Visible from H2o, the main menu option worked, but I still didn't like it, so I turned it off.
[Samsung Galaxy S21 Ultra] mapl.ph:
I couldn't emulate what you did. I already tried flashing G998U Verizon firmware. No n78 band, then reflashed again to G998U1 , still showing the same bands. I even tried G998W (Canada) , still the same.
[Samsung Galaxy S21 Ultra] kmdigital:
Hmm, I have no idea how/why I got the N78 band. Maybe because it sees ATT as the CSC, as that seems to be the key difference.
[Samsung Galaxy S21 Ultra] yygemmi770:
That's exactly how because N78 is operating frequency for ATT and not VZW.
[Samsung Galaxy S21 Ultra] Ptuk:
Does that mean you will get n78 if you flash att firmware from sammobile?
[Samsung Galaxy S21 Ultra] yygemmi770:
No. The CSC is what determines the bands used.
[Samsung Galaxy S21 Ultra] kmdigital:
Are you saying that you don't get the ATT CSC if you flash with this firmware, using the ATT (not Home) CSC?
[Samsung Galaxy S21 Ultra] kmdigital:
Question on a VZW sim. Does it need to be a 5g enabled SIM or would a 4g LTE suffice? Thx
[Samsung Galaxy S21 Ultra] mapl.ph:
I will try flashing G998U1_ATT (Android 12) over the weekend. Please note that I'm using Smart Telecoms in PH as my sim/network provider. Don't mind the bloat, just need the 5G connection.

1. G998U_ATT - no n78 band (Android 11)

2. G998U_VZW - no n78 band (Android 12)

3. G998W_XAC - no n78 band (Android 12)

4. G998U1_XAA - no n78 band (Android 12)
[Samsung Galaxy S21 Ultra] Abaddon:
G998U/G998U1 does not have n78 at all. 5G will not work in PH using that device since PH is only using n78
[Samsung Galaxy S21 Ultra] Ptuk:
If you read the thread you will see somebody has got n78 on this model.
[Samsung Galaxy S21 Ultra] mapl.ph:
Weird thing is when you install the firmware and on your first boot you'll connect to 5g momentarily. Happened twice now over U and U1 firmware. But when the phone ask you to reboot because of a network change you'll lose the 5g icon again. Couple of google searches also indicate that n77 and n78 was activated by AT&T last year on A12 system. So hopefully, it's all in the firmware. Will post results on the weekend as I have work and no time to redo everything from scratch.
[Samsung Galaxy S21 Ultra] Ptuk:
Tried att u1 android 12.....didn't work.
[Samsung Galaxy S21 Ultra] mapl.ph:
Did you try it without SIM first? I actually ordered at&t sim to be shipped here in PH. Will try use to activate then make a sim swap after the configuration. But it's going to take a while to ship.
[Samsung Galaxy S21 Ultra] Ptuk:
I took out the physical sim but not the esim. Should I remove the esim?
[Samsung Galaxy S21 Ultra] mapl.ph:
We can try. Hopefully it works.
[Samsung Galaxy S21 Ultra] mapl.ph:
@Ptuk , didn't work for me either. Looks like we need to wait for someone who knows how to do it via QPST. I still have my AT&T sim on it's way. Last ditch effort.
[Samsung Galaxy S21 Ultra] kmdigital:
Well, crud. Hopefully the SIM will do the trick.
[Samsung Galaxy S21 Ultra] mapl.ph:
When on download mode does it say ATT on your bootloader? Should be on the upper left part.
[Samsung Galaxy S21 Ultra] kmdigital:
Well, I got a brand new, unregistered 5g Verizon sim, but for whatever reason it's not updating the software to VZW. It also didn't request a restart, so I restarted it manually several times to see if that would do anything. Does anyone have any idea why it doesn't seem to want to update and how I can potentially get it to download and install the VZW software?

I sure would like to get it to update this, as I think it'd work better. For one thing, even though in certain areas it'll update to show 5G service, when I use an App to check what bands are actually in use, it's ALWAYS just the B2, B5 or B66 LTE bands, and I NEVER have any actual 5G bands in usage. In addition, what get's really odd is that sometimes , in some areas, when it says 5G and I check download speeds it's at a very anemic 2-3 MBPS, even though I have 5 bars. In other areas it'll say 5G, but I have good speed, however, it's still only using LTE bands, not 5G.

All this to say, I don't think I ever actually get 5G bands, for whatever reason. It's probably related to the CSC software being ATT/TMB, and not VZW.

Appreciate any ideas anyone can provide. I really don't want to flash to VZW firmware from U1, as from what I read, I shouldn't use Home CSC, and I really don't want to go through the hassle of resetting everything up again. That's a MAJOR pain.

THanks
[Samsung Galaxy S21 Ultra] Ptuk:
Sorry to hear this...Samsung spend a lot of time restricting the usefulness of their phones! I think I read somewhere that flashing to the Canada version (w) and then back to US might help with resetting a csc. By the way using samsung smart share on pc and Google back up makes flashing relatively painless. Have you tried the Quallcom tool to do it?
[Samsung Galaxy S21 Ultra] kmdigital:
Well, crud, I think I know what may be going on. Even though it's a 5G sim, it's also an LTE sim. Since it isn't activated, and since Verizon doesn't give you 5G access unless you purchase the correct data plan, it's only connecting to the network on LTE and not even trying 5G. Since 4G LTE is already perfectly functional and works like it should, there's probably no reason to download and install the VZW specific software.... I may be wrong, but in the SIM card status menu, it says LTE for both Voice and Data network types, which would seem to indicate that without the proper data plan it's locked to LTE.
[Samsung Galaxy S21 Ultra] mapl.ph:
@kmdigital , do you still have the box. Can you check whether it says AT&T on your box?
[Samsung Galaxy S21 Ultra] kmdigital:
The box for the phone? No, I don't have it, but I know that it was originally for T-Mobile, and probably about a month after I started using it with H2o, it updated the firmware and added the ATT software, as well as the ATT splash screen on boot up. Prior to that, it had the T-Mobile splash screen. Since then, I've changed the firmware to U1, but it's still stuck with ATT/TMB software, and there doesn't seem to be an easy way to force this to update.

Yeah, I suppose if I installed the VZW U1 firmware it "might" force this, but I'm not sure. But I don't want to do that because even though it's relatively easy to restore the apps, it takes hours to restore logins for various apps, etc, plus reconnecting bluetooth, etc. It's just a royal pain.
[Samsung Galaxy S21 Ultra] kmdigital:
Well, I FINALLY got this resolved by following the instructions listed below. I just finished flashing it to VZW, U and finally got it to switch to Verizon. Then reflashed with XAA U1 firmware, and IT FINALLY WORKS properly, actually even connecting to the NR77 C-Band. Previously, even though I had this band in the list, I would never actually connect to an VZW NR 5G bands, even though occasionally I would get a 5G logo, but then I had very slow download speeds compared with 4G LTE or LTE+. Previously, I also never got the 5G logo in my house, only LTE+, and now I have the 5G symbol. Previously, my CSC's were ATT/ATT/TMB/TMB, and now they're FINALLY VZW/VZW/ATT/TMB, so I should also be in good shape if I installed an ATT Sim. I do find it interesting that ATT stuck, but hey, at least I have VZW and it works far better than it did before, when I really was only on LTE even though I'd occasionally get a 5G logo.

The info below was exactly what I needed to get my original T-Mobile phone to finally fully switch to Verizon. And by using the Home CSC I didn't loses ANY data and I didn't have to restore everything, which is a MAJOR pain. And I even have the NR 78 C-Band as well for ATT, since that's still part of my CSC, not that I'll probably ever need it.

This info is from We1tFunk on Reddit

Final edit and "guide":

Updated: If you're already on Android 12 with a U1 and want to change carriers...you shouldn't lose data, but then again, always have a backup just in case:

Grab the latest build for both the U and U1 models. (Of this writing, that’s 4BUKF. The versions must match for this to work properly or you’ll bootloop.)

Put your phone into download mode. DO NOT FACTORY WIPE. Shut down your phone and hold both volume keys and the side key until you get the green screen. Hit volume up. You’re in download mode.

Grab Patched ODIN and flash the U firmware, making sure to use the HOME_CSC instead of CSC_OYM. (OYM will wipe your data, which we don’t want. If there is a USERDATA file, do NOT flash that, either.) Let it run and reboot your phone. Your phone will power cycle once, this is fine. (If your phone bootloops and lands in recovery, you flashed a mismatched version of Android and sadly will have to factory reset. Make damn sure the builds match!)

Once your phone boots, it’ll ask to reboot to switch carriers. Let it do this. Once the phone reboots and you see your desired carrier’s boot screen, you don’t even have to let it finish boot, you can hold Volume down and power until it shuts down. Either way, we want your phone shut down again.

Put phone back into download mode. You’re going to repeat step 3, but this time using the U1 firmware you downloaded. Again, make SURE you’re using HOME_CSC or you WILL factory wipe!

Phone should do the same thing it did, power cycle once and then go to optimizing apps and finally to home. If you pop into Settings > About > Software Information, Service Provider version should say your desired CSCs. (In my case, I went from TMB to VZW and it now reads VZW/VZW/TMB. The last one will never change, so don't worry about it.)
[Samsung Galaxy S21 Ultra] Ptuk:
Did you have to have the verizon sim in to do this?
[Samsung Galaxy S21 Ultra] kmdigital:
Yes, on the initial reboot I inserted the Verizon 5G sim and it asked if I wanted to switch to Verizon, and I clicked yes, at which point it shut down and then rebooted, restarting with the Verizon splash screen.
[Samsung Galaxy S21 Ultra] mapl.ph:
Do you still have the n78 band? I'm still waiting for my VZW and ATT sim to arrive.
[Samsung Galaxy S21 Ultra] kmdigital:
Yes, I still have N78 and N261 came back as well.

If you read the entire thread on Reddit, it seems that unlocked S21 phones that were originally sold by a specific provider don't do nearly as well auto-switching bands as the S20 did when they were flashed to U1. And regardless of what others say in regards to flashing firmware and making a U into a "true" U1, this isn't exactly correct. A vendor's phone, particularly TMOs, (and probably others) will ALWAYS have TMB in the CSC software, as well as others, even when flashed to U1. Flashing an S21 to U1 does NOT make it the same as a true U1, with XAA as the default CSC. I'm sure that Samsung can easily change any phone to a true U1, but just flashing the factory software doesn't do this, and apparently, flashing it to U1 also breaks the auto-switching capabilities that a phone normally has, hence the requirement to go through the process above to get it to work properly. Based on comments, with the original 4.0 release, the auto-switching worked again, but later updates broke this again. Also note that if I ever install a TMO sim in the phone again, it'll automatically undo everything I did above to get VZW as the CSC. This may or may not apply to all vendor phones, but TMO's for sure have this issue. Maybe someday someone will figure out how to flash the U1 and make it a TRUE U1, but my guess that's a Samsung internal thing that isn't readily available.
[Samsung Galaxy S21 Ultra] Ptuk:
I read (I think) you could do it by flashing to w (canada) and then back to u1....
[Samsung Galaxy S21 Ultra] kmdigital:
If you read the original thread on Reddit, that's what they first espoused. However, after doing further testing, it was determined that this wasn't necessary, and didn't really provide any benefit, as I recall because the original default CSC will ALWAYS stay as the last one in the CSC software string on any other than a factory unlocked phone. At least it's a great and easy work around by always flashing the Home CSC, the key being that all firmware versions MUST match in regards to the last 5 digits of the existing as well as replacement firmware (currently 5CVCB) for 4.1.
[Samsung Galaxy S21 Ultra] mapl.ph:
Just updating you guys that I have received the Verizon and AT&T sim but was not able to replicate @kmdigital 's situation. I was not able to get the n78 band. Upon insertion of the AT&T/Verizon sim it will apply the sim's network setting and you will be asked to reboot. Once done with the reboot, I'm unable to check the bands using *#2263#*. And once I insert my home network SIM (Smart Philippines) I will then be asked again to apply and reboot new network settings.

Tried the U firmware with AT&T/Verizon SIM, turn off, download mode, flash U1, then insert my Smart PH sim. It will keep on reverting to Smart PH Network settings.
[Samsung Galaxy S21 Ultra] kmdigital:
Just an FYI, a much easier, and I think better way, of checking available bands is with the Samsung Band Selector app by Raymond Wang from Google Play. It shows all currently available bands, plus the More Network Settings option provides some additional Settings that aren't available elsewhere. Hope that helps.
[Samsung Galaxy S21 Ultra] mapl.ph:
Thanks, my only dilemma now is if we have a way to not sync the new SIM when inserted so that it will use the previously sync SIM network settings.
[Samsung Galaxy S21 Ultra] kmdigital:
Yeah, I don't know of any way to prevent that, other than maybe using an MVNO on the same network that doesn't have the S21 on its approved phones list. That seems to have been part of the problem with Visible, in that the S21 isn't a recognized phone, so it doesn't necessarily automatically reboot with the correct bands, and why I first had to get it configured for VZW.
[Samsung Galaxy S21 Ultra] KxArt:
My phone is att phone, been using on starlight talk for a year or so. The screen broke. Got it fixed and no longer worked. I called straight talk they said Verizon bought straight talk I would need a Verizon sim. I got the sim in the phone and it asked me for network unlock code. Took me 4 days but got a code. The phone stopped prompting me for code so I used *7465625*638*# and entered unlock code. CODE successfull!!! OK so I reboot phone. My mobile network setting finally showed up. I chose the Verizon app in the app settings. Phone reboot again and all setting dissappear again. I would pay someone to help me get phone working again. I have more sim cards I purchased just don't know what I'm doing. Thank you.

Phone displays No sim No service with sim in.