iPhone 4s not activating fully with AT&T sim
What you describe is consistent with an iPhone that is still locked to AT&amp;T as the sole carrier. You can go to the AT&amp;T websites and fill out a form to see if the phone could be unlocked. If you can't get AT&amp;T to unlock the phone, then you could take that up with the seller of the phone or perhaps see about jailbreaking the device and unlocking it by force as opposed to by social convention.