Can't make or receive phone calls on an AT&T S20 Ultra

[userRLofioEJFo]

I have a two year old, AT&T cobranded Samsung Galaxy S20 Ultra, which as of today (4/30/22) can no longer make or receive phone calls:

• When I try to dial out, the phone immediately goes to "call ended", as if I hung up
• Incoming calls don't go through at all.  Moreover, the call hears that my mailbox isn't set up.  Normally, I used Google Voice for voicemail, and that had been working fine until today
• All other features, including data over wireless and SMS, work perfectly fine.  That is, these work fine when WiFi and Bluetooth are disabled, so it's definitely connecting over the AT&T network

Troubleshooting thus far:

• Tried rebooting the phone, going into safe mode, refreshing the connection from att.com/support
• The phone and all apps are running the latest versions available - no updates pending
• I removed the Google Voice app in case it was causing any issues
• I tried using the MMI codes (e.g., ##61#) to disable forwarding to Google Voice, but get a connection error (801) when sending the code
• Spoke with customer service on the phone and went through all their troubleshooting steps, including resetting network settings.  He eventually suggested I replace the SIM
• Went to at AT&T store and bought a new SIM, which didn't help.  They did mention they have had other customers in this week with similar problems with other Samsung phones.  However, I can't seem to find anything by Googling around

Current status:

• SMS and data work perfectly fine over the AT&T network (when disconnected from WiFi and Bluetooth) but still cannot make or receive calls
• Tried everything I can think of short of a full factory reset
• My wife's phone on the same AT&T account, and my work-provided AT&T phone, all work normally from this.  I've never had any connection issues in the past in this location
• Phone shows 5 bars for signal strength, and connected to a 5Ge network
• From the SIM card status menu, Mobile Network State = Connected, Service State = In Service, Mobile voice network type = LTE
• Phone = AT&T co-branded, network locked, SM-G988U

The guys at the AT&T store suggested waiting for AT&T or Samsung to push out a fix for the issue, since other people have had the same problem.  They said when they contacted the AT&T home office, the person they spoke with said they were aware of the issue.  However, I haven't been able to find anything online about it - you'd figure if it was a fairly widespread issue, there'd be forum posts or news about it somewhere.

Any suggestions on next steps?  Full factory reset isn't really an option - I'd sooner buy a new phone and make sure I've transferred everything successfully before wiping my current one.

[Cass94]

Okay just checking so first off do you have developer options enabled on the phone? If not go to settings>about phone>software info>and keep clicking on "build number" you will see a message bottom of phone click 3 more times to enable

[userRLofioEJFo]

yes

[Cass94]

Okay have you changed anything in there already?

[userRLofioEJFo]

You know what: I just tried something I should have tried before, but just now thought of it.

I swapped SIMs between my personal (broken) phone and my work phone.  The work SIM in personal phone worked perfectly; the personal SIM (that I got from the AT&T store today) in the work phone had the same error.

So, it's probably not a cache or setting issue on the phone, but a problem with either the SIM, or my account, I'd imagine?

[Cass94]

Wowww lol yeah if what you say is happening then it is for sure an error on at&t side on your account line for that number I'm just confused how getting a new sim didn't fix it though but definitely good to know it's not the phone....

[Cass94]

So your also saying the new sim won't work in your work phone either?

[userRLofioEJFo · Accepted solution]

Yeah, the new SIM on my personal account in my work phone was not working; the work SIM in my personal phone was.

With that info, I figured I'll try AT&T support again, since now I know it's something on their side... and lo and behold I got someone who knew how to fix it.  He re-enabled Voice over LTE... and yeah it works fine now 😛

Thanks for your help!  Glad I got it working again, without taking up your entire evening :).  I'll monitor it to see what's happening, but hopefully it's good to go now.

[Cass94]

Nice I didn't think you'd get any help from them this late lol crazy they could fix it that easy but they didn't see that issue earlier 😂

[Cass94]

It sounds like at&t will need to reset your account somehow the only thing I can think of that you could try to get your line to reset yourself would be going into your at&t account going to that phone numbers line and adjusting something(possibly adding then removing a feature) on that line temporarily and change back this should trigger the at&t system to send an OTA update to that lines sim access in the process hopefully it will replace the corrupt files

[userRLofioEJFo]

The fun part with AT&T support - I mentioned the "IMS not registered' issue to an earlier person, and they had no idea - insisted on going through troubleshooting.  This guy, as soon as I mentioned it he's like... "yep let me check... oh here it is."

It's completely a crapshoot as to whether you get a good tech.  I guess instead of going through troubleshooting repeatedly it might be better to politely end the call and try again.