Why to downgrade 4.3.5 to 4.1 iPhone 3GS?As most of you know that iOS 4.3.5 only have tethered jailbreak which mean that you have to connect your iPhone 3GS to PC every time you reboot it. When you downgrade 4.3.5 to 4.1 iPhone 3GS you will be able to get untethered jailbreak.
Required downloads to downgrade 4.3.5 to 4.1 iPhone 3GS:Download Ireb4.
Download - Part 1 - Part 2 - iOS 4.1 custom firmware (made by sn0wbreeze)
Download redsn0w 0.9.6 (mirror)
Download iTunes 10.4
How to downgrade 4.3.5 to 4.1 iPhone 3GS :Step 1: Run Ireb4 , your iPhone 3GS will enter dfu mode.
Step 2: Go to iTunes and flash 4.1 custom firmware ipsw.
Step 3: Jailbreak your iPhone 3GS with Redsn0w 0.9.6b6 - follow previous our guide - Click Here.
Step 4: Unlock your iPhone 3GS with ultrasn0w - follow our previous guide - Click Here.
Note: We have not had a chance to verify this guide, so if you gonna try it, please feed us back.
Update: Now you can make iPhone official factory unlock, you can check the details from here