Phone won't make or receive calls

@centaurus3200 Yep, our settings are identical. Updated to baseband version G973U1UEU6HVB2 and calling no longer works, data and texting are fine. Will try getting a new SIM tomorrow, otherwise I'm downgrading back to 11 to see if that does anything. AT&T support has been useless. Would've already hopped to another cell provider if I didn't have a discount and grandfathered unlimited plan.

@boggle  that is some weird stuff! what color is your SIM card?

@centaurus3200 One of the blue/white/orange ones, like below. I feel like I just replaced it but my concept of time is frankly rather poor these days. Really hoping it's something as stupid as that, I guess we'll see. Will report back tomorrow either way.

@boggle maybe it was just a coincidence, but before we all got android 12, one of the things i tried was to have the local ATT store swap to a newer sim. my old SIM was like yours... the new one is blue and white... and "5G". i really hope that fixes your problem!

i'd turn the phone off, insert the new SIM... then restart. maybe that will cause your phone, SIM and ATT's network to all talk to each other and "play nice" :-)

What is the 9th and 10th number on your sim

@GLIMMERMAN76 27

So it gets deeper. I get a new SIM card from the store and the guy says my account was still showing an IMEI for an old iPhone 5C I had used years ago (which would make sense why VoLTE wasn't working, just odd it coincided with the Android 12 update). He updated the IMEI number to my S10 but it has now removed my grandfathered unlimited data plan completely. Said there's nothing he could do in store and I'll have to call. Should've just lived with the 3G I had... AT&T isn't going to budge reinstating this plan, they've been trying to push me off it for a decade.

Victor in Tech Support CHAT was able to resolve this same issue I had with 2 of the 4 phones on my account.

@boggle man, just go to mint and call it a day imho. 

@centaurus3200 I have 5 lines and a sizeable legacy employee discount, so I'll have to price it out. Honestly just want to leave out of principle at this point. For $45 I wasn't throttled until 22.5GB and had UHD streaming. Will have to dish out nearly double to get this line back to what it was, (Edited per community guidelines).