Don't want to buy and unlock your iPhone youself? Then unlockediphones.com is a good place to look for new and used unlocked iPhones. Right now they have 26 models listed.
The Dev Team have announced that future release of an unlock for iPhone Firmware 1.2.0 that comes with the iPhone SDK. This will allow any application to be installed (jailbreaking) and any SIM card from any operator to be used (SIM unlocking).
All the gory technical details of the Pwnage project here.