AT&T has confirmed that the carrier will unlock iPhones for customers whose contracts with them have ended. This move would mean that the customers in question will have the freedom of changing their SIM cards and use their iPhones with other Telcos. While there have been other ways of doing that in less than legal fashion such as Jailbreaking, for those who didn’t want to stray from the narrow and straight path, they now can enjoy simple and legal way to free-up their devices.
Given that the only other major carrier that also runs a GSM network is T-mobile, while in the States, that seems like the only plausible alternative (unless you choose a smaller carrier) since Verizon and Sprint’s CDMA network will not be compatible with AT&T iPhones whether or not they have been unlocked. So if you have practiced the awkward conversation needed, you will be able to go to an AT&T retail outlet or unlock your iPhones remotely.