Side note on that, AT&T has always had a GB limit, even with the "Unlimited plan" of 5GB. It's in the fine print, but it's there. With the new options, it's even lower.

They do have a nice IPhone app though that will show you how much you've used as well as on their web portal. Also I've rooted my IPhone multiple times on a 3G and 3GS, so if people need help with those, I could probably assist, but the caveat is that if you ever upgrade through Itunes you'd lose your root. Buyer Beware :)