Phone won't make or receive calls

@formerlyknownas I bought it this week. 

@thehench

Change carriers.  It is not worth the amount of trouble AT&T will put you through to try to get this phone active on their Network - if it's even possible.

Same problem w/ unlocked S20 5G here.  Says IMS registration is missing and won't download the AT&T Updates, which I assume is the issue.  I thought the S20 was supposed to automatically detect the SIM and connect you to the right mobile network for updates.  I can clearly see that the firmware/CSC are all generic unlocked. 

Is there any way to trigger the phone to switch to AT&T?  Yesterday evening tried to get a new SIM at the store and I clearly knew way more than the personnel helping me.  Thank you.

Thomas.

I had the same issue until yesterday! My fairly new Galaxy S21 was not making or receiving calls since early August. Ask if the ATT representative can RECALIBRATE your phone to adjust to the new 4G network. This is what worked for me.

I have easily spent over 15 hours on hold and speaking with ATT representatives. I went in-person to the store and did a TON of troubleshooting. I had a case opened with IT which did absolutely nothing. I did countless network resets, tried a couple new SIM cards, even did a factory reset - all to no avail. 

I began receiving a text message after trying to call that read "We're sorry, but the phone you recently tried to use will not work on our network. Don't worry, make a call now to any number and it will be redirected to an AT&T representative to help you." 

One representative I spoke with lied straight to my face. She said my IMEI was not supported (after 30 minutes of troubleshooting) but I knew this was not true due to the many hours other representatives spent with me because my IMEI was supported and was not the issue. 

Finally I spoke with a representative who had the competence to note that it was most likely a network issue and that some phones did not automatically connect with the 4G network when they shut down the 3G towers. He suggested we recalibrate my phone, which required me to shut my phone off for 10 minutes while the recalibrating was done on his end. I turned my phone on and had my husband call me. BOOM. It worked. 

I cannot believe how many representatives I had to talk to to finally get competent help. Beyond frustrating. I hope you are able to find a solution!

I just left.
Using RedPocket on ATT network with same phone and no issues for less money.
Whatever....
(Edited per community guidelines).

I have a galaxy s9 quit receiving calls n texts about a week ago my carrier giving me the runaround I think it may be my apn settings but no way to find out. Can you help me

@Bradi

You indicate you using a different service provider. AT&T can't help you with a different carriers service. Most carriers have an IMEI check to determine whether your phone is compatible or not. Use your IMEI and search for different service provider or replace your phone.

https://www.att.com/buy/byod/identify?devicetype=phone