Alright killer there is a way around this. Played with my android last year and figured the way to bypass the charges.
Your going need a wifi available first.
First turn on airplane mode. Then turn on wi-fi mode so all you have is wi-fi available. Go to the market and download either easytether or pdanet. ATT has these apps blocked reason need the wifi. You can download both and try both see which you like better, they are both very similar. You will also need to download the software from their respective sites, just google pdanet and easytether. Once those programs are installed both on your computer and phone, you are all set to go. There wont be any charges for using these apps.
These tethering options are USB tethering but I believe pdanet offers bluetooth tethering if your computer has it.