Well, when we have the tethered Jailbreak for iPhone 3GS & iPhone 4, the support for the ultrasn0w on iOS 5.1 is still awaited. Not anymore because we now have an alternative for it until DevTeam come up with an update in few days. Needless to say, if you can’t wait to update your device on iOS 5.1 with preserved BaseBand, you can use this method for the ultrasn0w unlock. However, this doesn’t support the upgraded BaseBands.
The ultasn0w fixer 5.1 only supports the BaseBands given below –
If you have got any other BaseBands on your device, you either need to use Gevey Sim or wait for other solutions in future. The custom firmware for preserving the BaseBand on iPhone 4 & iPhone 3GS can be cooked either using Redsn0w or Sn0wbreeze. Once the custom firmware is created, put your device in PwnDFU mode and use Shift+ restore (Windows) or Option + Restore in Mac for the restore process to complete. Afterwards, you need to add this repository in Cydia – http://repo.iparelhos.com
You can add repositories under – Cydia>Sources>Edit>Add Source. After all the sources are updated, search for ‘ultrasn0w fixer 5.1′ and install it. The task doesn’t end here. Now, you need to search for the native ultrasn0w from the DevTeam and install over it for the unlock on iOS 5.1. As soon as you have performed all the instructions, your device would start receiving the signals of the respective carrier.
Did you face any issues? Let’s know in the comment section. We would definitely try to answer all of your queries.