Update : News from Twitter of MusclerNerd .

It seems that the baseband of the iPhone 4 had an anti-ultrasn0w protection that Planetbeing who works with DevTeam has succeeded to break ! Unlock tool for iPhone 4 iOS 4 is growing, then we will have an update of ultrasn0w when the jailbreak tool of iOS 4 will be released for all iDevices.

Note that our friend Geohot has given up his project to jailbreak iOS 4 for iPhone 4.

Be patient, the untethered jailbreak tool proposed will be like Spirit, easy to use and compatible with all iDevices, old and new iBoot.
No release before the update of the future update of iOS 4 (4.01? 4.1?) by Apple.