Unlocking an AT&T USA iPhone is rather easy if you meet certain criteria. AT&T Unlock is supported by this carrier and you can quickly request it from their website.
I will explain you here how to:
1) Request an AT&T Unlock for your iPhone (or other Smartphone),
2) Check if your iPhone meets AT&T’s Unlock eligibility requirements
3) Unlock your AT&T USA iPhone in case your unlock request is rejected Read more