ATT needs the user to subscribe a plan to use the tethering even though technically we don’t need to. The trick is that there is a small app will connect to ATT when you are trying to use the Mobile AP. It tells you “This account not setup for tethering, Please call ATT to have it activated”. Here is a way to work around this
You have to be rooted and use Terminal Emulator.
mount -o remount,rw -t yaffs2 /dev/block/mtdblk3 /system
Now enjoy the internet with your 3G network.