Unlocked Samsung S21 quit working...can only text now

This worked on a new to me One+7 Pro & my original phone a ZTE Axon 10 PRO.

I bought the One+ thinking all is good because it was on the whitelist phones.  It only allowed lte calling but no data.   The ZTE is not whitelisted so not sure if ATT will find a way to brick it again later.  /facepalm

I fixed this by adding a new APN with the following settings and I now have 4g lte voice and data on both phones

name ATT Phone
APN: phone
mmsc: http://mmsc.mobile.att.net
mms: proxy proxy.mobile.att.net
port: 80
mcc: 310
mnc: 280
apn type: default,mms,supl,fota,hipri
apn protocol & roaming: ipv4/ipv6
mvno: type none

@jimcrist - welcome to the nightmare.. There are multiple threads on these forums about unlocked phones suddenly not working, seemingly as part of this AT&T network upgrade.  Some of the phones have been working fine for a long time, and are on the "compatibility list" of phones that should work after the infamous network upgrade of 02/22/22.  But then they just stop working.

None of us really have the exact answers as to why it happens (that includes AT&T reps and customer support).  The only common thread is that all these phones appear to be unlocked phones not bought from AT&T.  Essentially, it looks like the BYOD program is no longer supported.

Some lucky people have been able to use some workarounds that others have figured out. The official AT&T debug suggestions have been unhelpful.  Some of us have been struggling for days (or in my case, periodically, for months).  Many of us have switched carriers - I'm doing that tomorrow myself.

If you want to stay with AT&T, your best option might be to just get another phone from AT&T directly, and sell your old one on Swappa.com or something.  Some of us have even been offered a free "upgrade" (usually an entry level phone) by AT&T.

Sorry to be the bearer of bad news. Good luck.

Last night I read that the key is to get AT&T to provision the phone for VoLTE.  Sounds promising???  Sadly, both the VoLTE setting and the Wi-Fi Calling settings don't even show up in my phone.  They do show up in my wife's Android Verizon phone.  Does this mean I have to get a repair shop to flash the firmware in my phone???

Mine is a Galaxy S21 5G (G991U1) with Android.

@jimcrist - you're referring to this one?:

https://forums.att.com/conversations/android/samsung-galaxy-will-not-make-calls-att-message-to-update-to-enhanced-lte-however-not-available/621579793ff7904fbc355dcb?page=2

This code *#*#4636#*#* reveals if VoLTE is active... however, mine was active (greyed out, though), and the phone still periodically stopped making/receiving calls, and instead rerouting me to customer service.  Customer service would temporarily enable the phone by applying a "remedy", but the phone would stop working again after a few days.

Now, my phone doesn't make any calls anymore - even the reroute to customer service isn't happening anymore. (I wonder if AT&T disabled my phone because I filed an FCC complaint...)

So, my point is that yes - the VoLTE provisioning might sound promising, but might not help you anyway.  And I've tried all the various tricks people have mentioned in the forums, but none of them have helped.  I didn't re-flash the phone, since mine was already updated, and VoLTE activated... 

I am switching to a different carrier as soon as I get the new SIM card in the mail.  Until then, I've resigned to the fate of AT&T not allowing me to make or receive calls, unless I buy a new phone from them.  I obviously won't do that, because the phone works fine, and I expect a carrier change to solve all my problems.

Good luck!

You have to buy a new phone. In the mean time switch your phone to 3g to make calls

I have the same issue but found an option to switch APN settings and with switching i can switch between calls or internet. But not both unfortunately.

https://forums.att.com/conversations/phones-tablets-devices/issues-with-att-on-my-samsung-galaxy-s21-5g-smg991u/622a6ddba30ea32d442089eb

@randumb00 

Buy a new phone, switch to 3g if you can (I couldn't), or save your money and take your perfectly fine phone to a different carrier. =)

AT&T is not the only option. There are pleny of others out there.

It's certainly important to have a properly working device, @jimcrist, @bobjungee, and @beachntrees! Here are a couple of steps that can help to resolve your experience.

First, make sure that the exact model of your phone is at least one of these supported devices: G970U*, G970U1*, G970W, G970F, G970F/DS. Please note that the model numbers marked with an asterisk will need to have their software updated in order to continue making and receiving calls.

To update your software version with models G970U and G90U1, follow these steps which are found at our Device Support Center:

1. Make sure your device is fully charged and connected to Wi-Fi.
2. From the device home screen, swipe down from the Notification bar and tap Settings.
3. Scroll to and tap Software update, then Check for updates.
4. Follow the on-screen prompts to download and install the update. The device automatically restarts once the new software successfully installs.

Besides software updates, customers have reported that the steps below have helped resolve their experience:

• Updating the SIM card. (To upgrade your SIM, visit your nearest AT&T Store.)
• Updating the APN settings following these instructions:
  1. Tap your Settings menu.
  2. Choose either Wireless & Networks, More Networks, or Connections.
  3. Tap Mobile Networks, then Access Point Names.
  4. Find and select the option to add a new APN. You may find a plus (+) symbol on the screen, or tap the menu button.
  5. Program each field using the settings found in the table.
  6. Save your changes to return to the APN's menu and choose the new APN.

If these solutions do not work, you may need to upgrade to an HD Voice capable device, upgrade your SIM, or both.

Also, please be advised that devices not sold by AT&T may not be compatible with all services. Even if AT&T sells the same make/model, a device sold by another carrier or by the device manufacturer may function differently.

We hope this info helps. Thank you for contacting AT&T Community Forums.

Lar, AT&T Community Specialist

Thanks for the reply, but it doesn't help.  We've been thru all that.  The S21 is a new phone that we bought in November because of the 3G shutdown.  $700 phone and $300 prepaid account and I've been without a phone for almost a week.  Unacceptable!!!

I hate how everyone is like you need to buy a new one from At&t. I just bought this phone a month ago and they aren't cheap. This is on At&t, not the customers who suddenly lost call functionality out of nowhere... especially when I asked a rep if an unlocked phone would work with no issues and they assured me it would work fine. Now it's just a pocket tablet because it can't make phone calls. I'm not going to reward At&t for making my phone useless by giving them more money for a phone I shouldn't need.