pepsi, first of all AT&T won't agree to cancel the dataplan even if your contract is over. I have tried myself calling them to cancel the plan after my contract was over. They didn't agree. They said if you are carrying a smartphone then you must have a dataplan otherwise just carry other phone. It is not only for iphone but it is for all smartphone. I know it sounds stupid but that is the truth about AT&T.
Correct me if I am wrong