Default FIX for Internet Explorer Not working in AT&T ROM Error
To fix the Page Not Found error in Internet Explorer -

go in to your Connection settings - click on Setup my Proxy servers - and REMOVE the check where it says "This network uses a proxy server to connect to the internet"
make sure you leave the Box checked where it says - This network connects to the internet.

and now Try connecting and browsing - it should work.

apparently AT&T customised their ROM to use their own Proxy Server.