Only 4 days after launch, the iPhone 3G has been unlocked using a special card that piggybacks to your SIM card. This fools the phone into thinking it's using an official carrier.
Of course, the fact that the iPhone 2.0 software was jailbroken so quickly pretty much indicated hacks wouldn't be too long in coming.
According to the one of the Brazilian hackers, Breno MacMasi:
Our procedure consist in using one SIM adapter to simulate a fake IMSI test card. Instead of the AT&T IMSI like in the universals.If you happen to be able to speak Portuquese, you can enjoy this video of the hack demonstrated: