HT1688: AT&T online supportLearn about AT&T online support
Currently Being ModeratedNov 26, 2012 11:00 AM (in response to Suken Shah)
iPhone: About unlocking - http://support.apple.com/kb/HT5014 - Only some carriers offer the ability to unlock iPhone for use on any carrier. Follow the instructions in this article to unlock your iPhone.
iPhone: Wireless carrier support and features - http://support.apple.com/kb/HT1937 - including a list of which ones offer unlocking.