Oct 24 2011
A lot of current iPhone 3GS or iPhone 4 users are using a Carrier locked device, having unlocked it using Ultrasn0w want to try out iOS5.
iOS 5 will upgrade your current Baseband thereby leading you to lose your Unlock.
Fear not, the latest build of Redsn0w will allow you to easily preserve your Baseband while still upgrading the Operating System to iOS 5.
The steps are fairly simple. Follow the guide below:
Things you’ll require:
1. Open up Redsn0w and Click on Extras.
2. Choose the Custom IPSW option and select your IPSW file.
3. Follow the steps on screen and you’ll get a Custom IPSW file whose name begins with NO_BB.
4. Open iTunes > Put iPhone in DFU Mode > Option + Click on Restore (for Mac) or Shift + Click on Restore (for Windows) and select that new Custom Firmware file with NO_BB prefixed filename.
5. Your iPhone should now be updated while preserving your old Baseband.
If you need to Jailbreak your iPhone, you can do it with Redsn0w itself.
Follow this guide to jailbreak your iPhone on iOS 5.