if they are activated to AT&T network first then u need to make sure u get them to unlock it (as long as the phone fully paid for, they do it in 24hrs).
usually for the latest model u cannot just buy it unlocked at AT&T but maybe for a 6s u can.
when the 7 came out i bought the AT&T ones the first day (didn't activate to AT&T network). then sold them and it worked normal.
limegreen wrote:fyi the ones i bought were at Apple store but AT&T
If you paid full price (~$699) then it will be unlocked. If you bought it on a plan and paid significantly less then it will be locked and in a contract.