MuscleNerd has confirmed that RedSn0w 0.9.5 Beta can jailbreak the pre-release of iOS 4.0 GM on the iPhone 3G for those with legit activations.

For those with legit iPhone3G activation on 4.0GM seed, redsn0w from 2 wks ago can JB your device.

RedSn0w 0.9.5 uses the same pwnage2 DFU-mode exploit that's been around since the 2.x days. Nothing new is revealed to Apple, and it's not applicable to the iPad. Don't go near it if you use yellowsn0w, ultrasn0w, or blacksn0w.

The iPhone Dev-Team also stresses that iOS 4 is only intended for developers with authorized access.