Downgrade iOS 4.1 to 4.0 on iPhone
Now that you have already upgraded to iOS 4.1. Now you want test some app on 4.0 or some feature is working in 4.0 and not in 4.0 . So here is the Method
Stuff you will need
Downgrade iOS 4.1 OS to 4.0 on iPhone 4, 3G & 3GS
1. Download iOS 4.0 firmware file.
2. Connect iPhone to computer
4. During the restore process you will get an 1015 error. Don’t worry, that’s normal. Just click on Ok and close iTunes.
5. Now open terminal on Mac/ Command Prompt on Windows and type following commands
. / iRecovery -s
setenv auto-boot true
Now unplug your iPhone and turn it off by pressing the home+power button
Once it is off, turn it on by pressing the power button. Plug-in your iPhone and load iTunes to continue with the activation
That’s it we have successfully downgraded iOS 4.1 to 4.0 on iPhone