Well, that’s not a surprise, iPhone OS 4.0 has been jailbroken within hours of release. MuscleNerd who is from the iPhone Dev Team released this video demoing Veency from the Cydia Store on iPhone OS 4.0:

Details on how to jailbreak iPhone OS 4.0 have not been released yet, but probably will be released when iPhone OS 4.0 is released. MuscleNerd has also said that the developer preview of iPhone OS 4.0 is quite buggy. Now, for those of you that are curious, Veency allows you to show your iPhone or iPod Touch screen on a computer. Veency is, obviously, for Jailbroken devices only and is free on the Cydia Store.