Lets say you have either iPhone 4 or 3Gs on hands and it is running Apple’s latest firmware: the iOS 6. Is it possible to unlock it? Yes and the answer once again is yes. With the release of RedSn0w v0.9.15b1 recently, you can now jailbreak iOS 6 tethered on iPhone 4 as well as installing Cydia. And once Cydia is there, you can use UltraSn0w Fixer to unlock your precious iPhone. Ultrasn0w Fixer for iOS 6 will only work for iPhone 4 and iPhone 3GS users, and supports the following basebands: 01.59.00, 04.26.08, 05.11.07, 05.13.01, 05.12.01 and 06.15.00. So make sure your iPhone has one of those baseband versions.
Anyway, here’s the way how to unlock iPhone 4 / 3Gs on iOS 6:
Launch Cydia, and hit Manage, then Sources.
Then 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.
Open the repo and browse to the Ultrasn0w Fixer for 6.0 utility.
Next, tap the Install button and let Cydia work its magic.
Next, download the latest official iteration of Ultrasn0w from Cydia.
Simply install this Ultrasn0w, after which, your work is done.
That’s all. Your iPhone should now be unlocked and you can use your favorite SIM card.