There's no need to start multiple threads in order to state the same thing. {Threads were merged.}

If its in the terms and conditions (which it is) AT&T can legally enforce it...

Data plan for iPhone is required for the life of your iPhone service and cannot be removed in the future.

AT&T is Apple's exclusive carrier partner for iPhone in the United States. An eligible data plan for iPhone is required. This data plan covers data usage in the United States and does not cover international data usage and charges. If AT&T determines that you are using an iPhone on your account without an eligible data plan, AT&T reserves the right to add an eligible data plan to your account and bill you the appropriate monthly fee.