H8sn0w has just released the new version of Sn0wbreeze 1.4. Sn0wbreeze is a jailbreak utility with functionality similar to PwnageTool. The new version supports firmware 3.1.3 jailbreak for the following devices:
Sn0wbreeze is a Windows application, so Mac users have to wait for the upcoming release of PwnageTool by the DevTeam. Alternatively, both Mac and Windows users can use Redsn0w to run jailbreak (no custom firmware though).
You can download the new version of sn0wbreeze
MuscleNerd continues to argue that we should not use sn0wbreeze. Especially users who have unlocked their iPhone with blacksn0w utility: