JailBreak iPhone 3.1.3
Jailbreak iPhone 3GS firmware 3.1.2 or 3.1.3 is now possible with the Spirit. Spirit is an untethered jailbreak for iPhone on the latest firmware. I have done it on my iPhone 3.1.3 and it is really a breeze.
First of all you need to download the Spirit Jailbreak software from the Spirit website and it is available in Windows, Mac OS and Linux.
Click here to download Spirit Jailbreak>>>
Jailbreak on MAC OS
This blog will give u a detailed tutorial on how to jailbreak your iPhone 3GS using the MAC OS.
Click here to the guide>>>
Jailbreak on Windows PC
This is a guide to jailbreak your iPhone 3GS on a Windows PC
Click here to the guide>>>
***Remember to do a sync with your iTunes before you start to do the jailbreak***