iPhone OS 4.0 “Beta” has just been released yesterday and today @MuscleNerd from the iPhone Dev Team already uploaded a movie on YouTube showing a jailbroken OS 4.0. Its probably done with Spirit which is an userland-jailbreak and will work on all OS versions. The userland-jailbreak is an untethered jailbreak.

We still have to wait till summer before we can update to OS 4.0 and jailbreak it, because OS 4.0 “Beta version” is only available to people with a developer license.

Source [iphoneclub]