Sn0wbreeze also know as PwnageTool for Windows, this tool will untethered jailbreak iOS on iPhone 4G, iPhone 3GS / 3G, iPod touch 4G / 3G and iPad without basebande update , setup custom boot logos, activate your iPhone, set a root partition size, build custom firmware, install SSH, and more.
[Updated for iOS 6.0.1 - 6 - 5.1.1 ]
PwnageTool allows you to restore to a custom IPSW file. For instance, you can restore to a pre-jailbroken firmware while simultaneously maintaining your current baseband (and thus your ultrasn0w carrier unlock). You can also add whatever packages you want in the “Expert” mode of PwnageTool, if you wish to pre-install Cydia packages.
[Updated for iOS 5.1.1]
The Apple server are closed ! time is over ! It dose not work any more
What do you need: A jailbroken iPhone that can be activated in iTunes (that is, not officially blacklisted), a computer with the latest iTunes installed and working internet connection. You will also need to know the carrier that your iPhone is locked to.This will unlock all basebands like 4.11.08 , 4.12.01 ,1.0.13 ,1.0.14,2.0.10
Updated with new solution
To unlock your iPhone 4 on iOS 5 with Gevey SIM you MUST update your iPhone 4 to pre-jailbroken custom firmware to preserve the unlockable baseband which are compatible with Gevey SIM.