UltraSn0w Fixer for iOS 6.0.1 has been released and now UltraSn0w Fixer for iOS 6.0.1 is compatible with the A4 iDevices i.e iPhone 4 and iPhone 3GS on the following basebands; BB 01.59.00, BB 04.26.08, BB 05.12.01, BB 05.11.07, BB 5.13.01 and BB 06.15.00. Remember that official UltraSn0w for iOS 6 is yet to be release by iPhone Dev team. If you rely on UltraSn0w unlock then you can unlock your iPhone 4 and iPhone 3GS with UltraSn0w Fixer for iOS 6.0.1 firmware BB mentioned above.
How To Unlock iOS 6.0.1 With UltraSn0w Fixer on iPhone 3GS & iPhone 4:
Step 1 : To use UltraSn0w Fixer for iOS 6.0.1 your iPhone 3GS and iPhone 4 must be jailbroken on iOS 6.0.5 firmware. You can follow this guide to jailbreak iOS 6.0.1 firmware.
Step 2: Add following repo in Cydia by going to Manage>Sources>Edit