Mysterious Blackjack II data usage charges?

I have an AT&T BlackJack II that I got about two months ago. I have never used the internet on it. No eMail either. I do use AIM though. Last month, the data usage charge was $125! The only thing I can think of that might cause that is me accidentally pressing the internet on a few times. But when that happens, I close out of it quickly. Does anyone have an idea about what might have caused this? I don't think it's AIM, because the IM's are through text messaging.But it could be. I don't know... help?