Ok so if I verify that the esn and imei are good I can unlock it even if I'm not the original owner. The reason why I'm asking is b/c the online form for unlocking a atnt phone asks for the account holders name, ssn and a bunch of other stuff that I wouldn't be able to provide if they asked me that in the t-mobile store. Don't want to get stuck with a t-mobile device.
https://www.att.com/deviceunlock/?#/unlockrequest