"Data Plan for iPhone includes unlimited data in the U.S. Access rich HTML email and desktop-level web browsing, as well as Visual Voicemail to listen to voicemail messages in any order you choose."
The above taken directly from AT&T's website. There is no heavy users on an unlimited data plan. End of story. Unlimited is just that.
As it stands now, don't cry when you advertise one thing and people use it as such.--
"Some people have no respect for logic."