Dev-Team has released updated version of Redsn0w for iOS 4.0 GM build, latest version is named as "0.9.5b5-1" and it brings support to jailbreak and enable multitasking and wallpapers on iPhone 3G and iPod Touch 2G, running on iOS 4. Apple disallowed these functionalities on both these devices, reason being the performance issues. Please read the notes carefully before using this version of redsn0w.
1. This version is for iPhone 3G, iPod Touch 2G users only, and it doesn’t hacktivate your phone. In simple words, your device wouldn't be unlocked after using it, so don't continue further if you want to use unlocked iDevice.
2. Our recommend is to wait for official public release of iOS 4, which is expected on 21st June.
3. It's for MAC users only.
The jailbreak procedure is almost similar to earlier releases of redsn0w, only difference is the added options of enabling multitasking and wallpaper, which you will see while execution of redsn0w. Just download Redsn0w 0.9.5b5-1 from here and follow our step-by-step guide given here to jailbreak iPhone 3G and iPod Touch 2G on iOS 4.0 GM build.
Update 1: Jailbreak iOS 4.0 with Redsn0w 0.9.5b5-2 on Mac | Windows
Update 2: Jailbreak iOS 4.0 with Redsn0w 0.9.5b5-3 [Hacktivated]
Update 3: Redsn0w 0.9.5b5-4: Fix iBooks Issues After iOS 4.0 Jailbreak
Update 4: Download Redsn0w 0.9.5b5-5 to Fix iOS 4 APN / MMS Issues