Developers of informal applications for jailbroken iPhones, msft.guy and zmaster, announced the release of new version of Ultrasn0w fixer for 6.0 to unlock iOS 6 on iPhone 3GS and 4. There are phones which are tied to a contract with the cellular operator so, you need to jailbreak it and than to unlock it. If you don't use Ultrasn0w because your baseband is not old the only way to unlock iOS 6 is using IMEI unlocking service. It is paid method but it worth it, so you can choose it right now and don't mess with any Ultrasn0w and jailbreak software. If before you could use launched Ultrasn0w by hackers from iPhone Dev Team, now third-party programmers were the first who released Ultrasn0w fixer 6.0 before Ultrasn0w. This latest version unlock iOS 6 on iPhone 3GS and iPhone 4 with old baseband versions. unlock ios 6 ultrasn0w You have to know that it is impossible to unlock iPhone 4 or 3GS with the new modem firmware using Ultrasn0w fixer. This solution is compatible only with the following baseband:
  • 01.59.00
  • 04.26.08
  • 05.11.07
  • 05.13.01
  • 05.12.01
  • 06.15.00
Ultrasn0w fixer for iOS 6 does not support baseband:
  • 02.10.04
  • 03.10.01
  • 04.10.01
  • 05.14.02
  • 05.15.04
  • 05.16.02
But first we must find out if you have don't one or even two things because if you don't - unlock won't work:

How to Unlock iOS 6 on iPhone 4 and iPhone 3GS

Step 1. After jailbreak you need to install Ultrasn0w fixer package from Cydia. So, open Cydia and go to manage Manage => Source. Step 2. Click on Edit and Add: 
http://repo.iparelhos.com
and click Add Source and wait till Cydia download all needed packages. Step 3. Click the Search and find official Ultrasn0w and install it first. Step 4. Only after you install Ultrasn0w you need to install Ultrasn0w fixer for 6.0. Step 5. Restart your iPhone 4 or 3GS but remember that your iOS 6 is jailbroken tethered which means that you have to boot it tethered using Just Boot option in redsn0w 0.9.15b1. Step 6. After rebooting just wait for the signal. Now you use your iPhone 4 or 3GS running unlocked iOS 6 with Ultrasn0w and Ultrasn0w fixer! Congratulations!