Following is the guide to downgrade your iPhone 3G and 3GS from firmware 4.0 beta 1 to firmware 3.1.3, This guide is tested on both Mac and Windows machines.
Step 1. Download iTunes 9.1 and Firmware 3.1.3, install iTunes 9.1 and place firmware 3.1.3 on desktop.
Step 2: Connect your iPhone via USB and put it in DFU mode (hold down the button “Power” and “Home” for 10 seconds then release just the power button).
Step 3: When your phone is in DFU mode manually install firmware 3.1.3 (by pressing Shift + Restore and select the firmware you downloaded previously).
Step 4: If you encountered an error message like 1011, 1013, 1015, just ignore them(Actually the firmware3..1.3 is already successfully installed) and use iRecovery to get the hold of your iPhone again.
1) Windows users Install libusb from the downloaded pack, Mac users can skip this step. If you are on Windows Vista / Windows 7 then follow the steps given below to install Libusb-Win32.
- Right click on this file. Select Properties | Compatibility Click the “Run this program in compatibility mode” box and select “Windows XP (Service Pack2)” from the drop down list.
- Right click again and select “Run as “Administrator”. Follow the installation instructions. Running the test program list the usb devices plugged into my computer – but not my new device.
2) Start iRecovery in Terminal / Console with
3) Execute the following commands:
- setenv auto-boot true
Step 5: Reboot your iPhone (keep holding home + sleep for 10 seconds).