Thread reported.

A simple search with these keywords "downgrading 3.0 to 2.2.1" reveal much info you can use to go about this. Also, this query can be posted at the centralised iPhone Club thread rather than making your own.

The general consensus here abhors hardware-unlock solutions like these because it involved many configuration of different sim-unlocks that may or may not work for the end user, hence why no one solution will work for all.