Here's good news for iPhone 4 users who've been waiting for a carrier unlock. The iPhone Dev Team has released an update to Ultrasn0w, its iPhone unlocking client, that's compatible with the iPhone 4. When run on an jailbroken iPhone 4, Ultrasn0w will allow you to use a carrier other than AT&T in the US.
It's a very simple process, as the video above demonstrates. Just note that jailbreakme.com is used in the demonstration, which makes use of a PDF exploit found in the iOS software. Also, jailbreaking your iPhone may void its warranty; proceed entirely at your own risk.
The Dev-Team first announced that they had been able to unlock the iPhone 4 last month, but only released the updated version of Ultrasn0w now. If freedom from AT&T is your thing, have at it.