A70 not working

That isn't a phone sold for the US market.  It is NOT on the ATT list, and depending on which model it is, it may work on T-Mobile or Verizon.  

The best site I could find for your phone is https://www.kimovil.com/en/frequency-checker/US/samsung-galaxy-a70

And that site doesn't consider VoLTE or carrier whitelists.  Just LTE bands.

Unlocked phones that will work on AT&T now that 3-g is going away

@kevink  My father got that phone from Walmart and we live in the US so it is a US phone.

@Ally52114

It doesn't matter where your father bought it. That phone was not made for the US market and will not work on AT&T. 

A70 models /varients

If you purchase it recently you should return it. Otherwise the options are to see if it will work on T-Mobile or to replace the phone someone that is on the list of acceptable unlocked phones.

Looked at Walmart.com, and at least among the 3rd party resellers there, no one apparently oversees whether the phones there are truly usable in the US.  GSM unlocked US Compatible doesn't mean it can be activated/used on ATT now.  I even saw 3G and 2G phones for sale there.

We'll be happy to clarify this for you @Ally52114.

As @formerlyknownas and @kevink have informed you, the A70 is not on our list of compatible devices. We'd advise you to return the device to the point of sale and buy a prepaid device directly from us that is guaranteed to work on our network.

Please let us know if you have any additional questions; if so, we'll be happy to assist you. Thank you for reaching out to our AT&T Community.

Darais, AT&T Community Specialist

Here's what makes all of this confusing...At&t was supposed to be shutting down 3G as of Feb 22 2022...however after speaking with a At&t representative over the phone on Feb 27-28 (early A.M. EST) At&t won't officially suspend its 3G completely until Mar 16. They are doing it in phases. The A70 seems to already have been affected...but another device...the Samsung Galaxy A20S...that also wasn't made for sale in the U.S. market...that also isn't on At&t official list of compatible devices after the 3G shutdown...that also carries the correct frequency bands as the A70 (  confirmed as B2, B4, B7, B12, B17, and B66...all At&t primary frequency bands for 4G/LTE(+)  [ though B17 is now dedicated for first responders])... and that is equipped with a toggle for activation of VoLTE built into the device... does...as of today... function on the network using LTE/LTE+ for making/receiving calls, sending/receiving texts, and accessing the internet. 

@Nicolas81

There are phones that should work and don't, and there are a lot of sounds that should not work and still are.

Means nothing if you're not effected

@formerlyknownas If that is the case... and I'm not claiming that it is...or isn't...then At&t should not have put out a list in any literature online... or as information for their representatives to give out to customers...claiming it as definitive. They painted the picture as if any device not on the list would be incompatible with the network.  They have also done a poor job of training their representatives on explaining the reason why certain devices should work but don't... or why devices that shouldn't do.  One representative told me over the phone that At&t was not ever going to fully shutdown 3G because too many people had old phones...and he was in technical support.  Most of them have never heard of any device not sold by At&t.. or not manufactured for the U.S. market...or even know what to explain frequently bands matter or what At&t primary bands are... leaving customers scrambling to figure it out for themselves... or just buy/receive a new phone... thus committing to At&t for the next 3 years..(depending what "free phone" is offered or that they are eligible for).  And supervisors only seem to be slightly better trained.  I don't blame them for it... I put that on the company.... the representatives are doing what they are trained to. 

I can't speak for the other customers...but my Samsung Galaxy A70MN accesses the internet and makes/receives text using 4G/LTE now...the only part that doesn't work is making/receiving calls.  The reason why I am mentioning this is that the phone did make/receive calls BEFORE the 3G shutdown using 4G/LTE... it never displayed a 3G/H/H+ before that. If it had... I would have returned it as soon as I bought it. I bought the phone in 2020...and was already aware of the pending 3G shutdown by all of the major carriers...and knew to use a current SIM card to test if a device not manufactured for the US market would work...looking for the 4G/LTE symbol when accessing the internet,  making/receiving text... and most importantly...making/receiving calls.