AT&T can do whatever they want with the data plans. They can tier it, restrict it, free it, eliminate it, whatever. Oh sure, the techie-blogosphere will be full of angst over it. But in the end, it's a business decision by AT&T.
If AT&T becomes too restrictive, people can exercise their right as a consumer, and simply choose not to do business with AT&T. If you have an unlimited data plan now, AT&T lets you keep it until you re-up your contract. At that point, you have the choice to exercise your right to NOT sign a new contract. It's really quite simple. If you don't like AT&T's prices or policies, then don't buy an AT&T phone. Period. No one is forcing anyone to buy that shiny new iPhone. Judging from the continuing supply shortages, the general public doesn't care about a few people's antenna gripes. The issue is being completely overblown by the technology media.