If you’ve been following iPhone hacker MuscleNerd on
Twitter, you would have seen that he has already worked
on a jailbreak for the iPhone’s new OS 4.0. The video demonstrates him
using both Cydia and Veency on his iPhone running the developer’s copy
of OS 4.0. There are no details about how to do the jailbreak and he
also recommends that users (with a dev copy) should not bother, because
the current version is "very buggy”. Take a look at the video below
demonstrating the results of the Jailbreak.