I just called them, and they said I'll be receiving an e-mail with instructions on unlocking it. They'll need your IMEI# and an e-mail address to send the instructions to.
http://9to5mac.com/2012/04/06/in-response-to-rising-number-of-complaints-att-is-unlocking-iphones/
Beginning Sunday, April 8, we will offer qualifying customers the ability to unlock their AT&T iPhones. The only requirements are that a customer’s account must be in good standing, their device cannot be associated with a current and active term commitment on an AT&T customer account, and they need to have fulfilled their contract term, upgraded under one of our upgrade policies or paid an early termination fee.
http://9to5mac.com/2012/04/06/in-response-to-rising-number-of-complaints-att-is-unlocking-iphones/