No clue. I know when I was with AT&T, I had a cheapie flip phone that I’d bought at Best Buy, but it was an AT&T Pay-as-you-go phone. Then I switched to a cheapie smart phone, and from there to Consumer Cellular. All I know for sure is that I’ve kept my phone number for 17 years and the phone I have now will work on AT&T’s network after they do whatever switch they do. Can’t ask for much more…
Sorry, I think we’re off track again… the CSR didn’t ask anything about my current phone. I got the idea that my current phone (a BlackBerry Key2) might not work in the future from the generic threatening email/text they’re sending out to customers, to wit:
[TEXT MESSAGE] AT&T FREE MSG: In Feb 2022, we’re shutting down our 3G network to make improvements to our network. We’re shipping you a new FREE cell phone to replace your device ending in XXXX. All you need to do is activate the new device. You’ll find setup information in the box. If you don’t activate your new cell phone, we will automatically activate it in approximately 30 days. Once your new cell phone is activated, your current cell phone will only be able to call 911 and 611 until Feb 2022. If you need additional assistance, visit one of our stores or call us at 800.880.8581.
Further research (shown immediately below) suggested to me that my current Blackberry Key2 is actually compatible with AT&T’s 4G LTE network (and likely to be compatible with new 5G network – don’t ask for a cite on that, because I don’t think I can find it again…):
BUT as I’ve said a couple of times:
I called the number at the end of that text (quoted above) and said “Don’t send me a new phone,” and the CSR said, “Ok.”
Perhaps, but I think this time I understood you, and may have said something unclear. I understand you didn’t talk to them about your current phone. I believe you should, however, to make sure you and AT&T are on the same page about your current phone and they don’t block it from the network after the cutover.
Thanks. My phone wasn’t a cheapie (but nowhere near what a new iPhone costs!), and it is an extension of my heart, soul, brain, and guts. I have it set up exactly the way I want it. It’s like a puppy that you have finally housebroken, that you’ve taught to do cute tricks, that you’ve persuaded to stop eating your best sandals, and that sleeps next to you all through the night. I don’t feel this way toward all of my (many) gadgets, but my phone is a pet. The perfect pet. (Although I have stopped short of naming it, so I guess I’m not completely nuts.)
From all the message boards I’ve been reading this afternoon, the upshot seems to be that if you phone AT&T and attempt to find out whether your phone will work after the switch, you will get multiple answers from multiple people. There probably is someone who knows the answer for sure, but I don’t know how to locate them.
I remember back when I was with Sprint, every time I called the customer service line, I’d get some fourth tier CSR and have to work my way up, telling my tale of woe over and over again. It was very hard to find anyone who knew stuff. One time I accidentally found a rep who really knew a lot! I had saved up many, many questions and asked them all. It was a rewarding experience.
In short, your suggestion is a worthy one, but I do not believe it is possible to ascertain that “you and AT&T are on the same page about your current phone.”
Well, sadly I’ve had a similar experience, and I think you’re likely right. One last thing I’ll throw out, though: Sprint’s customer service agents always struck me as unusually incompetent, so maybe you’d have a slightly better outcome with AT&T. Good luck!
Thank you for patiently trudging down this road with me… 
So, I wanted to applaud your research, issue one caution, and one correction. And yes, I used to do this sort of thing as a job, so semi-expert, even if it’s been a couple of years. So, first the caution, in that it should be compatible based on AT&T’s website, across 3 bands. This is by no means bad, but if in your specific area those bands are not present, or not readily accessible (due to position, etc), you may have weaker signal or less access than a ‘new’ phone. I wouldn’t buy new before it became an issue, but an advantage of a carrier phone is that it generally covers more bands that are used by that carrier. Again, a caution, probably unneeded as I would expect you’re already connecting on 4g/LTE currently.
And the correction, nothing I’m seeing on Amazon or Blackberry’s website says that phone has a 5g modem. Especially on a phone of that age, it would be . . . extremely unlikely. Especially since 5g is more a loose confederation of technologies that are currently almost carrier specific rather than a true standard. That’s not to say you need 5g. Heck I don’t need LTE most of the time, since at work and home I have wifi for both calling and web surfing. And I don’t see anytime in the near future (several years) before 4g LTE will be even considered for repurposing. So unless 5g is a desire of yours, I wouldn’t upgrade just for that compatibility.
The saddest words of tongue or pen (even though it eventually worked out for ThelmaLou). I was blatantly lied to by an AT&T phone drone, and wound up spending hours contesting a hefty charge for non-received service tacked on as a penalty for disengaging the slimy tentacles of AT&T and going to another company.
Never again.
@ParallelLines Thanks for your knowledgeable post.
I have no intention of buying a new phone. If I did (which I don’t), fortunately, I’m in a position where I can just buy a new unlocked phone outright. I don’t need to be in thrall to any carrier.
I’m only concerned if my BlackBerry Key2 will no longer work on AT&T’s upgraded network.
I came across this a few months ago:
This section seems pertinent:
Check if your phone is supported
It all very confusing, but luckily, there’s a way to check if your 4G LTE phone will remain connected after February 2022 without relying on AT&T’s list:
As recommended by Android Police, install a testing app on your AT&T phone.
Disable wifi and make sure you’re in a place with 4G LTE connection.
Run the app. If the “Voice Network Type” lists “LTE,” you should be fine. If it says anything else, you’ll need to upgrade before February 2022 in order to make phone calls (other features will still work, however).
So, to recap: Yes, AT&T’s 3G network is going away, but not until February 2022. Your phone will still work for at least the next 18 months, and in many cases, will remain active after the transition if it supports 4G LTE and HD voice. Don’t worry about AT&T’s list of supported devices, and instead use the test outlined above. Hopefully, AT&T’s future communications on the 3G shut-down will be clearer.
I installed the recommended app, called Network Mode Universal.
Here is a screenshot from my phone:
Yuck. That surely leaves you with a bad taste in your mouth.
It hasn’t necessarily worked out yet. 'Cause the Fat Lady hasn’t sung yet. Are we still allowed to say that? I’m still surveying the lay of the land and gathering information.
Yup, all looks good! Will cross fingers that nothing unexpected happens but you should be fine for quite some time to come.
Thanks, ever so!
But I may ditch AT&T anyway, just for shits & giggles. 
I’m on AT&T, and they have been sending me messages that the Samsung Galaxy I bought in Bangkok before moving back will not work after next February. They’ve not offered me a free phone though. I sort of wish they would.
Don’t take their word for it. Go to this link and investigate further.
FWIW, I saw this on reddit today in a thread on this topic:
FYI - I was told today by an AT&T rep that as long as your phone is 4G capable, it will still work in Feb, even if it isn’t on the whitelist.
I think @ThelmaLou has done amazing work on protecting herself, so she won’t need this, but for people who are potentially at risk and for existing T-mobile customers (I no longer work for them, but have in the past, so fair warning) who are having an issue or interested in 5G there is a very, VERY interesting promotion going on.
Basically, if you switch to T-Mobile you can get a number of deals, not surprising. There are normally very few if you’re an existing customer without adding a line, but right now (and for the last week, so may be going soon) you can trade in --any-- undamaged working smart phone for a new Nord N200 5G phone. It’s up to 4 phones per account, and has to be applied as an ‘upgrade’ to an existing line (so if you only have 3 lines, you can only get 3, and that line cannot have a current phone promo on it).
The phone is . . . decent? I would say cheap and cheerful, but with obvious compromises to get it to it’s normal $220 price range. And the promo works like a lot where you pay taxes upfront, get a monthly bill for 24 months and a monthly credit for the same 24 months, with you losing all credits if you leave before the 24 months are up. So it is a retention strategy. Personally I have a lot of lines (I cover myself, the spouse, my MiL and FiL, and my best friend and his mother) so I upgraded 3 lines to get 3 free backup phones.
Here is the link to T-Mobile’s Website and the phone, look for the magenta text for the details. Again, I don’t suggest this if you have phones you like, but if you’re worried about future compatibility and already on T-Mobile (and like me had a drawer full of obsolete phones you couldn’t GIVE away they were so old but still worked) they make great backups for the expensive phone you just dropped in the sink. 
WARNING WARNING WARNING: Please remember, these promos are rarely given fixed end dates, so if you’re reading this anytime after 7/14/2021 check the link and refresh to make sure it’s still in effect. Don’t risk being on the tab for the whole amount because the promo expired.
Thanks. My phone’s not on that list, it’s an old Samsung Galaxy J series, and I’ve had it for years. Definitely not 4G-capable. I’ve been thinking about getting a new phone anyway.
Funny thing is I’ve not received any e-mails from AT&T about this, just text messages.
My phone isn’t on the list either. I’m suggesting you do this exercise:
I’ve gotten both.
Thanks. I’ll do that.
From the OP:
UPDATE: Today I got an email that said my Samsung Note9 is on the way, including a tracking number. To quote myself: WTF??
ISTR that someone posted that they got a phone like this from AT&T, but now I can’t find it.
Of course, at the moment, my main phone is still in the shop and I’m using a $10 LG Tracfone (with a phone number different from my main number) that I bought at Best Buy last week.