After the recent release of jailbreakme, a jailbreaking tool for the iPhone and iPod on iOS4, the iPhone Dev Team has released the new version of ultrasnow as promised. Ultrasnow can be used on jailbroken iPhone 4s to unlock the baseband OS so that the phones can be used with any carrier except AT & T.
The application is accessible through Cydia once you jailbreak the iPhone on iOS4. Simply jailbreak your iPhone 4 on iOS4 by going to www.jailbreakme.com through Safari on the iPhone. Once you jailbreak the phone through the browser (which is pretty self-explanatory) you can unlock the iPhone by going into Cydia and adding the "http://repo666.ultrasnow.com" repository. After that its as simple as searching and adding "ultrasn0w 1.0-1". Restart your iPhone and the unlock will be complete.