The popular iphone jailbreaking tool balckra1n has been updated to RC version by Geohot. blackra1n RC2 supports jailbreaking of iPhone (2G,3G,3GS) and also iPod touch (1G,2G,3G) which is running the 3.12 firmware. Earlier you have seen the Pwnage tool used to jailbreak the iPhone 3.12 firmware. Blackra1n is know for its quickness in jailbreaking iphone. In short its a 30 second jailbreak iPhone tool.
Whats new in the blackra1n RC2 release.
Fixed Icy issues.
You can follow this guide on How to Jailbreak iPhone 2G/3G/3GS and iPod touch 1G/2G/3G running iPhone 3.1.2 Firmware with blackra1n.
Also you can follow this to Unlock iPhone 3G/3GS 3.12 Firmware with Ultrasn0w
Also if you need the 3.12 firmwares for iPhone download them from below.