iPhone 3GS on firmware 3.1 using this latest release. However Pwnage Tool 3.1.3 will only be able to jailbreak those

iPhone 3GS and iPod 2G who have already been jailbroken previously and will not work for those one with a 3.1 firmware just unboxed.

They have also provided a list of important points which you should consider to read before using Pwnage

1. If you are using a 3G iPhone with ultrasn0w and rely on ultrasn0w to obtain cellular service, then you should only upgrade to 3.1 with a PwnageTool created .ipsw.
2. PwnageTool will work for the
   iPhone 3GS assuming you have already Pwned it at 3.0 or 3.0.1
3. PwnageTool will work for the iPod touch 2G assuming you have already Pwned it at 3.0 or 3.0.1

Step by Step guide on how to Jailbreak

Download Pwnage Tool 3.1.3

http://apfelportal.de/host/images/PwnageTool__3.1.3.dmg
http://imodzone.net/pwn/PwnageTool__3.1.3.dmg
http://nevyn.nu/files/PwnageTool__3.1.3.dmg
http://zcr.me/f/PwnageTool__3.1.3.dmg
http://dl.opt-6.com/public/PwnageTool__3.1.3.dmg
http://mirrors.c2wifi.org/iPhone/PwnageTool__3.1.3.dmg
http://www.spiralnine.com/bin/PwnageTool__3.1.3.dmg
http://www.hackthatphone.net/PwnageTool__3.1.3.dmg
http://downloads2.touch-mania.com/PwnageTool__3.1.3.dmg
http://coldgame.de/PwnageTool__3.1.3.dmg
http://files.mackgoodstein.com/PwnageTool__3.1.3.dmg
http://dev.poorlad.com/PwnageTool__3.1.3.dmg