If you're a US service member facing deployment, you may be able to take your iPhone with you. According to MacRumors, AT&T has begun unlocking in-contract iPhones for deployed military, letting them use it with another carriers overseas. Although carriers are required to suspend phone service on request, this move would be above and beyond that mandate.
AT&T hasn't responded to us at this point with comments, but MacRumors says it's confirmed that the company has unlocked in-contract phones on request. If you're not in the military, AT&T will still unlock your iPhone as of a few days ago, but you'll have to wait until it's out of contract. For both groups, the process appears to be the same — just contact customer service with the request, though we're not sure what kind of checks are required for service members.