Phone cannot make or receive calls

@centaurus3200 

I'm going to T-mobile Monday... I hardly get two bars in my house (been here 14 years) anyways. It's time for a change

My parents are on board, it's just a little bit pain for them since they don't have un locked phones and my brothers is on a contract. 

Has anybody with a dead phone tried the Samsung band selection app or force lte only app on their dead phones? Both are on the play store. 

Not sure if forcing the phoned to only use lte networks will work, or nothing would happen because you still need to somehow turn on HD voice? 

I have an S20 5G - SM-G981U. 

Based on  https://www.att.com/idpassets/images/support/pdf/Devices-Working-on-ATT-Network.pdf.

My device should work.  It doesn't.  Was on the phone with tech support for almost 2 hrs, went to the ATT store for another hour until they closed to get a new SIM after they ran out of things to try over the phone/air, still doesn't work.  Everyone checked my phone model, and it is on the verified list.  Going to have too call tech support again tomorrow I guess.

Can't someone figure it out?

Hate to tell you this bud. Your phone is not going to work. I have a s21 that doesnt work. This is a deliberate and unethical business practice by att. They are purposely shutting down unlocked phones that werent purchased from them. Thats fine i will take my business elsewhere. 

@HoppaWang

@Jtbuilder25

Reset your network settings. Then go back into settings and make sure it's set to voice over LTE.

If your phone is on the list there is no reason it should not work on AT&T.

Re Firstnet users! 

The list of phones for firstnet is different! If you are a firstnet customer, AT&T cannot install the packet for First Responders on an unlocked phone..  the only way to get an unlocked phone working on firstnet is to flash AT&T software

@Jtbuilder25

That's incorrect.

AT&T has a list of unlocked phones that will work on their Network that is as long as the list of their own phones. 

Non carrier, unlocked phones that will work on AT&T

If you are a first net customer, you must have an AT&T phone, or flash AT&T software onto an unlocked U1 model. 

AT&T cannot install the firstnet packet required for preemption and priority on unlocked phones. 

@formerlyknownas, can you please explain how to set it to VoLTE?  I'm pretty familiar with my phone but never been able to find that exact setting through any menu even though I've been looking for it for a day now.  I do have developer mode enabled and I've definitely reset my network settings at least 15 times yesterday so I know to do that after any network change.

On a side note, I did find out that I can make calls on 3G or 2G think because the new SIM they gave me has a new APN "agms" that my old one didn't.  This allows me to make and receive calls but I get no data.  Switching back to the original APN I was on "ATT Nextgenphone" gives me LTE but no calls.  There's no way that I'm going to be switching back and forth to used my phone and I'm pretty sure that's not what they intended.

Maybe it would help if I attached some pics.  This is what I had in the APN.  

@HoppaWang

Flash the ATT software.

I suspect your s20 was from a different service provider, and it did not have the proper update to unlock att software.

APN deleting aren't going to work

@formerlyknownas,

You're absolutely right so I appreciate any help.  This device was a new unlocked S20 5G without ATT software.  How do I get ATT software (I hate bloatware, but if it's the only way to work)?