iOS4 for iPhone and iPod touch is just released, and its still available only for developers right now as the official version is yet to go live. But till then you can use the firmware in your iPhone 3G, iPhone 3GS and a team has successfully tried to jailbreak the iPhone 3GS with the iOS4 firmware, using the Pwnagetool tool. Still, you are doing it at your own risk, as the baseband preserving is not guaranteed fully. Btw thanks to Amit Bhiwani and tranfx for these instructions.
The bundles included in this release are not official because they were not issued by the DevTeam.
You must be on already pwned 4.0 Beta / 3.1.3 / lower.
Use this guide on your own risk, we are not responsible for any damage (if any).
How to jailbreak the iPhone 3GS using iOS4 :
1. Pwnage Tool 3.1.5 [Mirror 1] [Mirror 2]
2. iPhone 3GS iOS 4 GM Bundle
3. Instructions to add custom bundles data.tar
Step 1. Right click on Pwnagetool.app and open “Show Package Contents” and then browse to the following location – Contents > Resources > Firmware Bundles – and at this location, copy the custom jailbreak bundles that you have downloaded.
Step 2. Now right click on the Redsn0w.app and open “Show Package Contents” and browse to the following location – Contents > MacOS > and from here copy the Cydia.tar.gz to your desktop and extract its contents.
Step 3. Now the cydia you extracted, have to be copied to Pwnagetool. Right click on Pwnagetool and open “Show Package Contents” and then browse to –
Contents > Resources > Custom Packages and here right click on ‘Cydiainstaller.bundle’ and hit “Show Package Contents” and hit the Files area, and here overwrite all the files from the ones you extracted from the redsn0w.app
Step 4. As the normal procedure is done to create the custom firmware, you will just have to open the Pwnagetool and make the custom firmware.
Step 5. After the custom .ipsw file is created, you will have to replace and restore the iOS4 through your iTunes 9.2. Put the device in recovery mode and restore.