The downgrade has been made possible thanks to an exceptionally hard-working developer that goes by the name MuscleNerd, I’m sure you have heard of him. He has released an updated version of Redsn0w which allows users to use the tool to downgrade your 06.15.00 baseband to 05.13.04.
As with all tutorials please backup your device and proceed at your own risk. ConsumingTech will not take responsibility for any loss of data or damage that occurs to your device during the tutorial . This method has been designed for devices running on a 06.15.00 baseband only and will not work on any other devices.
The iPhone Dec Team has even issued a warning to those iPhone 3GS users that are currently running the latest bootrom, please read:
“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!”
Procedure:
Step 1. First you will need to download the current (and relevant to your OS) version of Redsn0w.
Step 2. Once downloaded you need to unzip the compressed folder then save it to somewhere easy to locate such as your desktop.
Step 3. You will need to download the IPSW file of the iOS which your device is currently running. To check what iOS your device is running you can tap on ‘Setting’ > ‘General’ > ‘About’ > ‘Version’. Once you have downloaded the IPSW file save it somewhere you can find it easily.
Step 4. Using the Redsn0w folder you extracted in Step 2, Launch the Redsn0w tool and select the ‘Extras’ button in the Redsn0w box.
Step 5. Select the ‘Select IPSW’ button. Once you have done this you will need to navigate Redsn0w to the IPSW file that you downloaded in Step 3. Select the required file then press ‘Open’.
Step 6. You will then be asked if you have a new or old bootrom iPhone 3GS. It is critical at this stage that you follow the on-screen instructions word for word, as completing the next few steps incorrectly may brick your device or wipe all your data.
Step 7. Next select the ‘Jailbreak’ option from Redsnow’s main screen. This step can take some time as the Jailbreaking data has to be prepared. Once done a list of options will be displayed.
Step 8. You need to select the ‘Downgrade from iPad baseband’ & ‘Install Cydia’ options. If your device is Jailbroken and has Cydia do not worry about selecting this one. Then click ‘Next’.
Step 9. Your device will need to be disconnected from your PC and turned off at this stage. It will then need to be put into DFU Mode. You will be able to follow the on-screen instructions to do this, don’t fret if you have to try more than once. Then in your own time, click ‘Next’.
Step 10. Redsn0w will start downgrading your baseband once the device is in DFU mode and you have pressed next. This step can be rather lengthy too, it’s important to remember not to touch your device during this time. Just let Redsn0w do its thing.
Step 11. Once it’s done, your device will reboot. It will be on the unlockable baseband and you will be able to use Ultras0w from Cydia to unlock the device.