Now that iPhone 4 has been launched in US, and in some European countries, with lots more to follow in July and August. What everyone is obviously waiting for is to jailbreak and unlock the iPhone 4. Since iPhone 4 comes unlocked in almost all countries except for United States, what everyone really wants is a jailbreak, which requires a new exploit as Apple has already patched all the holes in the most recent firmware release, including the one used by Spirit.
The official ultrasn0w unlock is now available for iOS 4 which works on all basebands including 05.13.04 and 05.12.01 on iPhone 3GS and iPhone 3G. Since there is no jailbreak available yet for iPhone 3GS with new bootrom, you cant unlock it as even though the baseband is unlockable. This is because unlock relies on jailbreak. So if you have an iPhone 3GS with new bootrom and you rely on an unlock, it is best to avoid iOS 4 (formerly iPhone OS 4) for now.
In a reply to a tweet, MuscleNerd of iPhone Dev Team has confirmed that iOS 4 (formerly iPhone OS 4) is confirmed to be unlockable, and probably so is the yet to be released iPhone 4. What they have actually got this time around is a new exploit for the latest 05.12.01 / 05.13.04 basebands, which they have been saving for months for a major new update - the time for which has now come.
