Last week I had experienced unlocking iPhone 3GS with iOS 4.2.1, Baseband 5.14. For now, the only solution you can unlock is update the Baseband to 6.15. And when you update to 6.15 you can’t downgrade this baseband to stock, meaning you lose your warranty, since apple will know that you’ve been jailbroken. (I warned you…)
The UltraSnow 1.2 unlock does not support the 4.1 or 4.2.1 baseband that comes with those iPhones. The only way to unlock them is to update them to iPad’s 3.2.2 baseband 06.15 which is fully compatible.