Thanks to the iPhone dev team and MuscleNerd, now the users of iPhone 3G and 3gS can downgrade the baseband from 06.15.00 to the previous one, having full unlock and GPS support. It is welcome news since the launch of iOS 6 will help in making an extensive use of the device’s GPS capabilities. If you are looking for a reprieve from the 06.15.00 baseband and its limitations, then the salvation to 05.13.04 has now come.
Before you start the process, you need to know that this method will work only on those devices which have 06.15.00 baseband running on their devices, which primarily includes iPhone 3GS and iPhone 3G. This method will not work for iPhone 4 or 4S users. Also, in case there is some real sensitive data on your devices, you might want to consider backing up your device in case something goes wrong during the process.
Also Apple has issued a warning saying that if your iPhone 3GS has 134 as its digits 3-5 in its serial number (xx134…), then one should NOT try installing the 06.15 baseband as it will break the radio. This will prevent both the downgrade from working and the normal software of the iPhone from using it as a phone.
Step By Step Guide to Downgrade iPad 06.15.00 Baseband To 05.13.04 iPhone Baseband
Step 1: Download the latest version of the Redsn0w tool which is 0.9.14b1( Mac/Windows) making sure that you have the correct version of the above said tool for your OS.
Step 2: Now you need to unzip the contents of the downloaded compressed files and save them on your system in some known location.
Step 3: Download the IPSW file for the iOS that is working in your device. This can be checked by going to Settings>General>About>Version. Once download is done, you can save the file in a familiar location.
Step 4: Launch redsn0w tool and click on the Extras button on your screen.
Step 5: Click on the select IPSW option and point the Redsn0w to the IPSW file that you had downloaded in step 3 above. If you are running iOS 5.1.1, then you can point it towards that said firmware. Now click on Open after finding the required IPSW.
Step 6: Redsn0w will ask you if have an older bootrom iPhone 3GS or a new version, so read the instructions carefully.
Step 7: Go back to the main screen of Redsn0w and click on Jailbreak. After the preparation of jailbreak data, which might take a while, you will get a set of different options.
Step 8: Check the Downgrade from iPAd baseband and Install Cydia Options and then click Next. If you have a jailbroken device and have Cydia installed then you don’t need to check the option.
Step 9: make sure that your device is power off and unplugged. Read on-screen instructions on how to put the device on DFU mode, once that is done, click on Next.
Step 10: After going into the DFU mode, Redsn0w will do its thing and proceed with the downgrade of the baseband, this might take a while. Do not touch your device during the process of downgrade.
Step 11: If everything has gone fine, then you iPhone will reboot and it will be on the unlockable 05.13.04 baseband. Now you can use Cydia and use latest version of Ultrasnow for unlocking your device.
There it is then. In these simple steps you have successfully completed the process of downgrade of the baseband for your device.