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.
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