If you did it through iTunes then you'll need to go back to 2.2.1 using the Pawnage tool.
Step 1: Get the 2.2.1 Firmware, just Google it, you'll find it easily. Go to the Pawnage tool and create a custom firmware. Put your iPhone in restore mode and on iTunes press "Option + Restore" and the select the custom firmware you created.
Step 2: After that repeat these steps with the 3.0 firmware.
If you did it through the Pawnage tool just do Step 2!