iPhone OS 4 GM is available for developers and it’s already leaked in the wild. If you downloaded those GM builds and now you want to go back to OS 3.1.3 or lower for whatever reason, we created a step by step guide for iPhone 3G and 3GS running on iOS 4 GM. iOS 4 is still in GM and you needn’t to edit your host files for iPhone 3GS to bypass Apple signatures.
iPhone 3GS users : Apple stopped signing OS 3.1.3 signatures so you need to modify your host files to downgrade iPhone 3GS with Cydia SHSH, so follow the instructions posted in following link.
Instructions to Downgrade iOS 4 GM
Step 1: Download and place OS 3.1.3 / 3/12 on your desktop, now put your iPhone in DFU mode with following instructions.
- Connect your iPhone to your computer.
- Turn iPhone off.
- Hold power and home together for 10 seconds (exactly).
- Release power but keep holding home until the computers beeps (observed on a PC) as a USB device is recognized.
- A few seconds later iTunes should detect your iPhone.
- If the Restore Logo is present on the screen, you are in Recovery Mode, not DFU.
Step 2: Once your iPhone is in DFU mode following message will be appeared in iTunes.
Click on “OK” , Now hold Option key (Mac) and Shift Key (Windows) while clicking Restore in iTunes and browse the OS 3..1.3 / 3/.1.2 firmware for your iPhone 3G or 3GS. Now the restore process will take 10 – 15 minutes.
Step 3: After restore process if you encountered an error message like 1011, 1013, 1015, just ignore them(Actually the firmware is already successfully installed). To exit recovery mode download Recboot, once you finishes your download launch Recboot app and hit the “exit recovery mode” button.
- Recboot for Windows : http://bit.ly/9he64R (Requires .Net 4.0)
- Recboot for Mac :
But if you encountered with error message like 1601, 1602, 1600 or anything else then try putting the iPhone into DFU mode and try again.
Stay tuned with us for your daily dose of iPhone news, you can follow us on twitter via @ihackinjosh You can also subscribe to our daily free e-mail news letter and keep your self updated with the latest of iPhone community.