I doubt it. Keeping the phone locked to AT&T means many consumers who don't want to mess with a jailbreak and unlock will continue service with them.Prediction... iPhone not exclusive to AT&T (when that is going to be is a great guess), you will see them unlocked following a contract.
AT&T has no legal obligation to unlock an iPhone, or any phone for that matter.
Now Apple on the other hand, could offer a permanent unlock after the exclusivity deal is over.