Dev Team has rolled out Redsn0w 0.9 beta which could be used to jailbreak iPhone OS 3.1.2. This beta release of jailbreaking tool works for iPhone and iPod Touch whereas it does not support iPod Touch 3G.

See also:
Sn0wbreeze to Jailbreak iPhone OS 3.1.2
RedSn0w & UltraSn0w Tools to Jailbreak/Unlock iPhone OS 3.0.1

Redsn0w 0.9 beta is available for Windows and Mac OS X systems separately, which you may download from the following integrated link.

Download Redsn0w 0.9 Beta