How to downgrade iPhone 3GS Baseband

For one reason or the other one need to downgrade baseband. As of this writing, iPhone 4/4S/5 can't have their baseband downgraded once upgraded through a stock IPSW restore.

However, iPhone 3GS can have its baseband downgraded.

Follow these steps to achieve a baseband downgrade for the iPhone 3GS.

Step 1

Download the latest version of Redsn0w on your computer and extract to your desktop.

Step 2

If your device is on iOS 6.1 or 6.0.1, you will still need to download 6.0 IPSW because that is what Redsn0w can support for now. Connect your device to the computer and let Redsn0w detect it.

It will also notify you of the device's bootrom and firmware version just at the bottom of the window

Step 3

Click on Extras, click on Select IPSW menu and the select iOS 6.0 IPSW that you downloaded. If you have a newer bootrom 3GS click yes

Step 4

Go back and then select Jailbreak. Kernel will be patched and then a window will appear where you will check "Downgrade from iPad baseband". Check it

Step 5.

Put your phone off and follow the instructions to enter into DFU mode.

Once in DFU mode, Redsn0w will proceed with the jailbreak and downgrade of your baseband.

Step 6

Once done, the remaining process will conclude on your device. Your device will reboot and your baseband will be downgraded.

Step 7

Go to Cydia to download ultrasn0w fixer and ultrasn0w 1.2.7 to unlock your device

That's it folks. Hope this helps someone. Leave a comment if you have any question.