Fixer is a jailbreak utility for iOS 6 that will only work for iPhone 4 and iPhone 3GS users, and supports the following basebands:
Compatible Devices :-
iPhone 4 (Jailbroken)
iPhone 3GS (Jailbroken)
Step 1: Launch Cydia, and hit Manage, then Sources.
Step 2: Next, add the iparelhos repository. If you’ve been organized and re-added your sources from iOS 5, then it should already be there, but if not, select Edit and Add, and type http://repo.iparelhos.com before hitting Add Source.
Step 3: Now, download the latest official iteration of Ultrasn0w from Cydia.
Step 4: Now browse for Ultrasn0w Fixer for 6.0 utility in Cydia. Tap the Install button and let Cydia work its magic.
That’s it! you should now have an unlocked iPhone.