Unlocking enables users to use any SIM on their device. Ultrasn0w which is a popular free unlocking tool does not works with iOS 6. Good news for unlockers as UltraSn0w Fixer is being released in Cydia which will enable Ultrasn0w work in iOS 6.
If you are unaware Ultrasn0w is a free unlocking tool by iPhone Dev Team and Ultrasn0w Fixer is a Cydia package which works with Ultrasn0w to unlock iPhone 4 and iPhone 3GS on selected basebands.
Official Ultrasn0w is expected to be updated by iPhone Dev Team sometime soon.
Ultrasn0w fixer for iOS 6 supports following basebands -
01.59.00, 04.26.08, 05.11.07, 05.13.01, 05.12.01 or 06.15.00.
How to unlock iOS 6 With UltraSn0w Fixer
1. Jailbreak iOS 6 if not done yet. You should remember that Ultrasn0w Fixer has support for iPhone 4 and iPhone 3GS only.
2. Launch Cydia. Go to Manage Tab >> Sources >> Edit >> Add
add the iparelhos repository: http://repo.iparelhos.com
3. Once you add the iparelhos repository you will have to install official version of UltraSn0w.
4. After installing official version of Ultrasn0w, install UltraSn0w Fixer for iOS 6 to your device. You will have to install official version of Ultrasn0w first and then Ultrasn0w Fixer.
You have unlocked your iPhone.
You will have to preserve your baseband while updating your device to iOS 6.