According to the Associated Press, there is a small loophole for those who are already AT&T subscribers. There is a catch, but it is possible. First, it's important to know that this only works if you had the unlimited data plan at one time.
Anyone who had an iPhone before June may be able to switch back to have unlimited data usage. This is because they were part of the unlimited data plan before the terms changed. If those users call and complain to AT&T, and maybe throw in a "Verizon is offering unlimited data" or something like that. You may be able to get back on that unlimited data plan.
AT&T won't discuss the specifics, and claims to handle these on a case-by-case basis. We aren't sure what your chances are of getting back your unlimited data plan, but it may be worth calling AT&T and complaining if you want it that badly.