I've had an AT&T iPhone since the beginning, and have lived through their dicking around with their data plans. I was fine with the 200 MB plan and switching to the 2 GB plan when I go on vacation and consume a lot of data. With their latest data plan revisions, I will be locked out of my current 200 MB plan if I ever try to temporarily switch to a plan with increased capacity, and would have to switch back to the 300 MB plan which is $5 per month higher.
I live in a rural area that is slowly being upgraded to 3G. I propose the following: AT&T's data limits should only apply to 3G service. Anything downloaded over EDGE should be free. If you run out of your limited data plan, you should be able to switch to EDGE and download as much as you want. Texts should be free or something reasonable like $5 per month for 1,000 messages, not $20 per month for an unlimited plan. I'm tired of paying $80 per month for a phone I seldom talk on in order to get a limited data plan and texting capabilities.
Since I know they won't do this, I'm planning to switch to one of the MVNOs once my contract is up. Either Republic Wireless if they open their beta again, or TracFone's "bring your own phone" program which recently launched (yes, it uses AT&T's network, but at a lower cost to the consumer).