In the video below you can see how to jailbreak your iPhone easy with PwnageTool 3.1.4 on firmware 3.1.2

Prepare -- The stuff you need

1. PwnageTool 3.1.4

http://downloads2.touch-mania.com/PwnageTool_3.1.4.dmg

http://download.sourcekills.com/PwnageTool_3.1.4.dmg

http://old.bielsipod.de/Daten/PwnageTool_3.1.4.dmg

http://www.hackthatphone.net/PwnageTool_3.1.4.dmg

http://miphone.ca/iphone-dev/PwnageTool_3.1.4.dmg

http://www.appleturk.net/ATWT/PwnageTool_3.1.4.dmg

http://www.apfelphone.net/dl/PwnageTool_3.1.4.dmg

http://apfelportal.de/host/images/dev-team/PwnageTool_3.1.4.dmg

2. Firmware 3.1.2 or the for your iPhone 1gen (1,1) iPhone 3G (1,2) iPhone 3GS (2,1)

get them from here

3. Follow the instructions on the video

* when you click restore for in iTunes you need to hold option/alt!