Carrier Unlocked AT&T phones compatible with which carriers?

[ssledoux]

I know unlocked AT&T phones are NOT compatible with all carriers. Which ones are they compatible with?

I had someone buy my daughter's XS, but now I'm unsure if it's compatible, and even though I put it in the listing for the buyer to verify, I am not sure he did.

 

[VineRider]

All carriers that do not use CDMA(sprint and Verizon) should work. However, as long as they are in LTE coverage Verizon should work. Not sure about sprint. T-Mobile should work fine as well

 

[ssledoux]

I think he's T-Mobile, so that's good. Now if AT&T will just get off it and let me do the unlock, that will be nice. Paid it off last week and the "system hasn't caught up." Idiots.

 

[Freakonomics101]

At some point in the near future, CDMA won’t even be a factor. After that, all GSM/LTE.