The iPhone Dev Team have just announced on their blog that their ultrasn0w carrier unlock now supports the iPhone4!
If you have not jailbroken your iPhone 4 yet then be sure to head over to JailbreakMe.com and do that first.
Then fire up the Cydia app, which will be installed on your iPhone 4 during the jailbreak process, and search for “ultrasn0w”.
Do bear in mind that there is a very small chance you can brick your iPhone during any of this, and Apple may not smile too kindly on your efforts.
If you jailbreak and unlock your iPhone 4, or any iPhone, do let us know how it goes in the comments…[Dev-Team Blog]