Earlier, we shared a post that geohot was the first to release balckrain/blackra1n tool for Windows for jailbreaking iPhone(2G, 3G and 3GS) and iPod Touch(1G, 2G and 3G) on the latest iPhone firmware 3.1.2. blackra1n tool for MAC OS X has been released now.
Process for jailbreaking iPhone and iPod with blackra1n is almost similar for both MAC and Windows. All you need to do is to download MAC version of blackra1n tool and follow the step-by-step procedure we shared here about jailbreaking iPhone 3.1.2 with balckra1n on Windows.
NOTE: We still recommend to use Dev-Team tools for jailbreaking/unlocking. By using PwnageTool 3.1.4 you will be able to unlock your iPhone, if you jailbreak via blackra1n, then you won't be able to unlock, blackra1n is recommended for those only who are on official supported carrier services like AT&T etc, and they don't need to unlock their iPhone or iPod Touch.
Update : Jailbreak iPhone 3.1.2 with blackra1n RC2
Have a look at these posts regarding jailbreaking/unlocking 3.1.2 firmware:
