Fez - only the 2G phones can be software unlocked (as in, unlocked to use on a different network other than O2). The 3G, regardless of firmware revision, cannot be software unlocked as of yet. There are hardware unlocking methods (rebelSIM, turboSIM, Any-Network sim adapters) but these are unreliable at best, and most don't work after (iPhone) firmware updates.

Also, anyone with a 3G phone that might want a software unlock in the future, is advised NOT to upgrade to 2.2 and use WinPwn to jailbreak it, as it may well render it completely non-unlockable in the future (something to do with baseband modification)