you might just want to ask someone at ATT because its my understanding that the data packet for the iphone is different that just a generic data package. Im sure it will work, but I think you might be able to save some money.
not trying to contradict the other poster, I'd just check on something like that. I dont think there is any harm in asking them in just a generic fashion. I dont have a data plan since my iphone goes back and forth w/ me from China so I generally avoid talking to AT&T. Nonetheless, good luck.