News via http://blog.iphone-dev.org/post/9018...grow-ultrasn0w

We’re happy to tell you that our ultrasn0w carrier unlock now supports the iPhone4!

Version 1.0-1 of ultrasn0w works for:

iPhone4 baseband 01.59
3G/3GS basebands 04.26.08, 05.11.07, 05.12.01 and 05.13.04
(If ultrasn0w doesn’t show when you search Cydia, add the repo: repo666.ultrasn0w.com)

Here is a nice howto video from @TechTechManTV that shows the process on the iPhone 4.