In a reply to a tweet, MuscleNerd a member of the iPhone Dev Team has confirmed on Twitter that iOS 4 can be unlocked with the exploit that they have preserved. He also added that the same exploit may be used to unlock iPhone 4 too. So it is confirmed that iPhone 3G and iPhone 3GS on iOS 4.0 are confirmed to be unlockable. The same exploit can be used to unlock 05.12.01 and 05.13.04 basebands. So once the iPhone 4 is released to the public we can expect even the new unlock tool to be released.
So if you are one of those who has been eagerly waiting for to unlock 3.1.3 on 05.12.01 baseband then you might get an answer very soon. Once iOS 4.0 is available to the public the Jailbreak Community will be able to release a final version of the Jailbreak and Unlock tool for iOS 4.
