I quit AT&T last year and went to tmobile just because of this behavior. They will scan your IMEI and determine if you have a smartphone (IMEI can tell make and model). Then they will "automatically" add a dataplan to your bill without even notifying you (except when you get the bill). Tmobile however does a no-contract, plus if you get the minimal data plan, I have four phones and am only paying $100 / month. And their dataplan works such that you get 500MB per month of the high speed access, but after you use it up, it doesn't charge you money, they just spam you with a text, then your speed drops to 2G.