Musclenerd tweeted this fascinating article about the first semi-realistic unlock solution to come from a non-dev-team source in a long time.

Singularity: Unofficial Review: Gevey iPhone 4 SIM hack

Summary: It's real (but won't work for some carriers & countries), expensive, slightly cumbersome and potentially legally risky - especially if you live in a country where 112 is actually a valid emergency number.

Personally, I agree with the article author, if you can, then you should wait for a proper solution from the iPhone dev team.