Apple recently released iOS 4.1 Beta 1 for developers. Those who have access to iOS 4.1 Beta can upgrade their compatible iPhone and iPod Touch to iOS 4.1 Beta. If you have upgraded to iOS 4.1 but having problems and wish to downgrade back to iOS 4.0, you can do it without the need of saved SHSH blobs because Apple has not started to sign iOS 4.1 as it is still in beta. Here is how you can downgrade iOS 4.1 Beta to iOS 4.0 on iPhone 4 and iPhone 3GS: 

  1. Connect your device to Computer and turn it off.
  2. Now you have to enter your device in DFU mode. To do this, hold power and home button together for exactly 10 seconds and then release the power button but keep holding home button until USB device is recognized.
  3. If you see the restore logo, that means you have not entered the DFU mode. When you enter DFU mode, the following message appears on iTunes.
    restore
  4. Click OK and restore your device to iOS 4.0 firmware by holding Shift Key (Windows) or Option Key (Mac), Clicking restore and browsing the iOS 4.0 firmware file. Following are the download links for iOS:
    - iOS 4.0 for iPhone 3GS
    - iOS 4.0 for iPhone 4
  5. After restore, you need to exit recovery mode. Do it with Recboot (download it here for Windows and download it here for Mac). After downloading, run Recboot and simply click “exit recovery mode” button. You need .NET framework 4.0 to run Recboot on Windows.  
[via iHackintosh]

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