I think the problem is that Windows/Microsoft uses Wi-Fi and ATTCM uses GSM configurations.
Windows or IE8 does not care what flavor of connection you have to the internet.
Cable, DSL, dial-up modem, or wireless - GSM or Edge - its all the same to Win7 and IE8.
So the problem is at a more basic level. Can you reach ANY webpage when you're connected to the internet?
Type this IP address into your IE address bar and see if you can reach MSN.com webpage: 184.108.40.206