Supported Devices for iOS 3
iPhone (original), iPhone 3G, iPhone 3GS and iPod Touch (1st, 2nd and 3rd generation)
Purplera1n was one of the original iOS3 jailbreaks, the current website is called Blackra1n
PwnageTool is your other choice to jail break iOS 3, here is their tool.
Here is a video showing how to jailbreak iOS3 with pwnage tool.