Here come blacksn0w to break all the barriers surrounding your iPhone firmware 3.1.2 and let it free. The much awaited blacksno0w is released by the iPhone hacker team Geohot that unlocks iPhone 3G and iPhone 3GS running on firmware 3.1.2.
For detailed step by step instructions on how to use the application to jailbreak the iPhone, read the post Unlock iPhone 3.1.2 Firmware with blacksn0w by Raymond pie.
Please note that this version of blacksn0w does not jail break the older versions like iPhone 2G. This application is intended for only iPhone 3G and iPhone 3GS users.
Happy Jail breaking :)