AT&T is shutting down its 3G network next February and is prepared to give its customers a new phone for free lest their current one becomes useless —that is, they can't place calls over LTE. Just don't expect the carrier to go to great costs for your replacement.
Mobile subscribers recently received the latest in a string of emails about the 3G shutdown telling them about the free phone offer. All they have to do is head to att.com/AcceptMyPhone, verify their phone number, and then they'll be able to arrange for the new phone to arrive in a few weeks.
The new phone customers will get is the AT&T RADIANT Core. It was introduced as an option for the comapny's prepaid customers in October of 2019 with an MSRP of $70 (though it's half off at the moment) and comes with a 480p display, a single 5MP rear camera, 16GB of storage (it takes a 64GB microSD card, though), 1GB of RAM, a removable 2,500mAh battery, and Android 9 Pie (Go edition). Hey, at least it has VoLTE.
I don't think we can recommend putting in an order for one of these, even as a lark. For nearly everyone affected, this will be a downgrade from their current devices, at least on paper. There are plenty of supported devices on AT&T's official list that you might be able to snag somewhere for less than $150 if the need arises.
Alternatively, the carrier could've just given credits toward a new phone. Guess it needed the help clearing its inventory of RADIANT Cores.