Up until this weekend, many iPhone 3GS users running the 3.1.3 iPhone update were unable to jailbreak. iPhone 3GS was not entirely jailbreak-proof. You may have noticed that there were no directions for jailbreaking iPhone 3GS’s running iPhone update 3.1.3 in my Ultimate Guide to iPhone Jailbreak. After months of hacking, a member of the iPhone Dev Team has released a jailbreak for all iPhones, including 3GS’s running 3.1.3. The jailbreak is called Spirit, and it works on iPad, too.
Windows and Mac OS X users, jailbreak your iPhone with Spirit.
Note: I have not tried to jailbreak my iPhone 3GS with Spirit. I don’t endorse this product. Jailbreak at your own risk.