Correction, the 2.2 FW has now been made unlockable.
Once you Jailbreaked your iPhone 3G with QuickPwn and installed Cydia, look for the yellowsn0w application, which will unlock the 2.2 FW for you.
This was realeased by the Dev Team just after New Years.
btw, my 2G iPhone came from the US, bought it off eBay when they first became available and using my 7-year old vodafone contract SIM in it with no issues whatsever, running 2.2 FW too.