iPhone OS 3.1.2 software update is the latest firmware released to all iPhone models. But, most of the iPhone users never update their iPhone straightaway until there is a stable and liable tool that supports iPhone 3.1.2 jailbreak. Whenever there is a new iPhone OS released, there will be a new update for the existing iPhone jailbreak tool or a new tool developed.
iPhone dev team had updated their pwnagetool (version 3.1.4) to hack and build the custom firmware using iPhone OS 3.1.2, which can be restored through iTunes to your iPhone. The iPhone will be jailbroken once the iTunes restore has completed. However, pwnagetool is only available for Mac OS and not all iPhone users are using the Mac PC.
On the other hand, GeoHotz had released his latest iPhone jailbreak and unlock tools recently to the iPhone community, which are available for both Windows and Mac OS. Blackra1n jailbreaks a clean firmware restore up to iPhone OS 3.1.2 and blacksn0w unlocks iPhone baseband 05.11.07 for iPhone 3G/3GS.
Have you updated and jailbroken your iPhone OS 3.1.2? Which of the iPhone jailbreak tool you have used?