MMS support...
if AT&T's GSM/MMS set up is anything like anyone else's, then they need to set a flag to say "this subscriber can receive MMS messages". Indeed, there are reports all over the interwebs that other AT&T customers already send and receive MMS just fine.
So it sounds more like a mass re-provisioning issue (and, working out how they're going to charge/fleece their iPhone subscribers: O2 deduct 4 from the SMS allowance for every MMS, or somewhere around 25p. Ouch... and to think people were complaining that the iPhone couldn't support MMS, and that email with pictures was not acceptable!)


