If you have an AT&T iPhone which is off-contract then you can unlock it permanently by sending a form and after 5-7 days AT&T’s tech support will contact you and “take it from there.” According to TechCrunch AT&T iPhone users can unlock full price AT&T iPhone by just restoring it via iTunes. Folks at TechCrunch explains that you can skip the paperwork and the wait time, because the phones are already saved as ready to be unlocked in AT&T’s database.
TechCrunch wrote on their website:
We have confirmed the process with AT&T’s technical support and successfully tried it with a T-Mobile SIM card. After restoring the device in iTunes, the user is prompted with the usual unlocking message: “Congratulations, your iPhone has been unlocked.”
Likewise if you have purchased AT&T iPhone 5 then you can fully unlocked by restoring it via iTunes. Users can also confirm the unlock by inserting a non-AT&T nano SIM card into iPhone 5 after restoring it.