Go here on your iPhone
http://help.benm.at/help.php
Go to mobile configs and select your provider. Accept the carrier file and reboot. You should now have a tethering option listed in Settings-General-Network. It works plug and play on PCs or Macs. MMS is touch and go as you need to trick ATT into giving you a normal NON iPhone texting plan to get it working.
I can verify that tethering works 100% however.