Jay Freeman (Saurik), the developer behind the infamous Cydia store for iPhone has found a way to downgrade iPhone 3GS from firmware 3.1 to firmware 3.0. This process will only work for those who have saved their SHSH to Cydia Server, for more on SHSH, read the complete detail blog post by Saurik here. Also to note here is that while this method will help you downgrade your firmware from 3.1 to 3.0, your baseband will not be downgraded which means you cant unlock it for now.
iPhone 2G and iPhone 3G users can follow the guide posted here in order to downgrade firmware 3.1 to 3.0.1.
Step 1: Download iPhone firmware 3.0 for iPhone 3GS. (Download link given below).
NOTE: Don’t use iPhone firmware 3.0.1 because Saurik’s Server currently does not have signatures for it.
Step 2: Download and install iTunes 9 if you haven’t already.
Step 3: Navigate to C:\Windows\System32\drivers\etc\ and locate “hosts” file.
Mac users can get to “/etc/” directory by going through “Go->Go to Folder” from Finder.
Step 4: Open this “hosts” file in Notepad (for Windows) or TextEdit (for Mac OS X) and add this
line as shown in the screenshot below:
Now simply save this file and you are good to go!
NOTE for Windows 7 and Vista: Start “Notepad” with Administrator privileges by right clicking on “Notepad” app, and click on “Run as Administrator“ option.
Step 5: Connect your iPhone to your computer and put it in DFU mode by: Hold down the power and home buttons for 10 seconds, letting go of the power button but continuing to hold home until iTunes recognizes the device with the message: "iTunes has detected an iPhone in recovery mode. You must restore this iPhone before it can be used with iTunes.". At this point your iPhone screen should be entirely black.
Step 6: Start iTunes, press and hold shift key and then click on “Restore”.
Select the firmware 3.0 .ipsw file you downloaded in Step 2 and restore it. During the restore process, iTunes will throw you 1015 error which will say:
The iPhone “your iPhone” could not be restored. An unknown error occurred. (1015)
Just ignore this error and restart the restoring process from Step 5 to Step 6 until you get the 1015 error again. At this point, simply ignore the error and close iTunes as your device has already been successfully downgraded to firmware 3.0.
Step 7: You can now jailbreak your iPhone which you have downgraded from firmware 3.1 to 3.0 by following the step-by-step jailbreaking guide posted here.
If you are a iPhone 2G or an iPhone 3G user then you can follow the guide posted here in order to downgrade firmware 3.1 to 3.0.1.
Feel free to ask me any question regarding any problem that you may encounter during the downgrading process.
Download iPhone OS 3.0 firmware for iPhone 3GS
Download iTunes 9