Downgrade 3GS/3G 06.15.00 to 05.13.04 Baseband for GPS + ultrasn0w

iPhone Dev Team announced baseband downgrade option in new redsn0w 0.9.14b1 , to get rid of iPad’s baseband 06.15.00 on your iPhone 3G & iPhone 3GS. After downgrading you can use fully supported GPS which you are not able to use on 06.15.00 iPad’s baseband.

This downgrade is not supported on iPhone 4 & iPhone 4S users. This is only for users running 06.15.00 baseband on their iPhone 3G & 3GS.

Warning from iPhone Dev Team:

If you have an iPhone3GS and if digits 3-5 of its Serial Number are 134 or later (xx134…), then you should NOT try to install the 06.15 baseband on your 3GS! It will brick your radio, preventing both the downgrade from working and normal iPhone software from using it as a phone! Be warned!

Here are the steps for downgrade:

• Download redsn0w 0.9.14b1 for Windows & Mac.
• Download the stock IPSW file of the iOS which you are currently running.
• Run redsn0w and click ‘Extras‘ button.

• Now click ‘Select IPSW‘ button and select your IPSW file. For Example , If you are running iOS 5 then select your iOS 5 IPSW file.
• Now redsn0w will identify your IPSW file.

• After that redsn0w also asks you if you have old bootrom of iPhone 3GS. Read the instructions below.

• Now go to Main window and select ‘Jailbreak‘.
• After that you will see bunch of options, select ‘Downgrade from iPad baseband‘

• If you have already using jailbroken device then you don’t have to check ‘Install Cydia‘.
• Now entering into DFU mode, Turn Off your device and plugged in to your PC. Click Next.

• When you successfully entered into DFU mode redsn0w will detect it and starts fetching required baseband files. It takes long time to at this step so be patient.

iPhone Dev Team also said about this step:

THIS STEP TAKES A VERY LONG TIME to complete and there won’t be any feedback while its running. Please just let it be for the next 3-8 minutes! When the ramdisk has done its job it will reboot the phone on its own.

After that rest of the process run on your iPhone. iPhone will reboot once and you have now successfully on 05.13.04 baseband.

Troubleshooting:

If you’re still using ultrasn0w after going down to 05.13.04, many people have reported that re-installing Mobile Substrate and/or ultrasn0w fixes crashes and “No Signal”.