It's the moment that many of you have been waiting for: the Dev-Team's ultrasn0w carrier unlock for iPhone 4 is out. You'll find version 1.0-1 of ultrasn0w in Cydia on jailbroken devices. If not, just add the repo666.ultrasn0w.com repository. It works for iPhone 4 baseband 01.59 and 3G/3GS basebands 04.26.08, 05.11.07, 05.12.01 and 05.13.04. If none of this makes sense then you've got no reason unlocking your device in the first place, buddy.
Update: No-nonsense video embedded after the break showing how to jailbreak and unlock. Easy peasy. [Thanks, Adam]