Jailbreak for Apple iPhone 3G and iPod Touch 2G running on iOS 4 is available to download. The iPhone Dev team has released an update for Redsn0w which will jailbreak your iPhone 3G and iPod Touch for iOS 4.
Redsn0w 0.9.5b5-3 is the latest version of Redsn0w jailbreak program and it can jailbreak iOS 4 software. Currently it is able to jailbreak iPhone 3G and iPod Touch 2G but expected to get an update to jailbreak iPhone 3GS for iOS 4 very soon.
Also Read: Apple iOS 4 Jailbroken for iPhone 3GS
Redsn0w 0.9.5b5-3 is available to download for Mac and Windows. Here is the download link to get the ZIP file for this program.