I used to work for T-mobile, we had a guy come in once who's son had run up a 3,000 dollar bill, the son sent something like 10,000 text messeges in the time span of a month, i forget the exact number but i remember wondering how it could be humanly possible to send that many text even if you were texting non stop 12 hours a day. but there was nothing we could do for him, it stated what the fees were for going over your text allowance were right on his contract, and the son went WAY over.
oh, and from actaully working at a cell phone company, i can say, NEVER trust a cell phone salesman, they will do anything and everything to get you to sign that contract and get their commission, I saw some fucked up stuff when i was at t-mobile.