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.


For those who can legitimately activate to the iPhone3G 4.0GM seed, the “point to previous IPSW” redsn0w trick works and will jailbreak your 4.0GM. The “trick” is to point redsn0w at the 4.0beta4 IPSW instead of 4.0GM (do this after you've updated to 4.0GM and activated through the new iTunes 9.2 on your Mac). Since the carrier unlocks aren't yet supported at 4.0, don't do this if you use yellowsn0w/ultrasn0w/blacksn0w. Many JB apps are still pretty buggy in 4.0, so again this is mostly useful only for developers of those JB apps.