good question. You could use this phone if:
1. the phone is unlocked from you other provider.
since it is GSM you do have the ability to use it on AT&T network provided it is unlocked. Now if its not unlocked then the phone will not accept the sim chip from at&t so then you need to contact you carrier that had this phone before and ask them to unlock it. you need to give them your IMIE number and some relevent information on your account.
Say you bought it from Ebay"
Chances are the ball is not in your court and the phone is locked and the merchant just got away with your hard earned cash, because you going to need to dig in the wallet to have a tech unlock it for you.
So the answer to your questions is YES and NO
Thanks and please do leave ratings or comments before you leave. Btw, I’m available to help over the phone in case u need at
https://www.6ya.com/expert/edwy_1a56970cf1ea4620