Preview at WWDC likely in June, followed by September launch.
AT&T Will Unlock Off-Contract iPhones Starting Sunday, April 8
AT&T issued this statement to MacRumors:
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.Last month, 9to5Mac reported that AT&T had agreed to unlock a user's off-contract iPhone 3GS under a "special one-time exception" after the user sent an email to Apple CEO Tim Cook about the issue. AT&T had previously refused to unlock the device, which the customer wanted to continue to use after moving to Canada, but relented after being contacted via Cook's office.
There have been many different hacks to unlock iPhones over the years, but this policy change will make it extremely easy for AT&T customers to legitimately and permanently unlock their iPhones for use on any network.