Redsn0w 0.9.5b2 download has been released to jailbreak iPhone 4.0 running on iPhone 3G which is a fix to a couple of bugs found in Redsn0w 0.9.5.
Some developers were facing SMS and 3G data failure issues after using Redsn0w 0.9.5 to jailbreak iPhone 3G on iPhone OS 4.0 beta 1. But a quick fix has been posted by the iPhone Dev-Team to jailbreak iPhone 4.0 on iPhone 3G.
Redsn0w 0.9.5 has been released to jailbreak iPhone 4.0 OS. This is not a complete and final version to use. iPhone Dev Team released Redsn0w 0.9.5 a couple of days ago for the iPhone OS 4.0 Beta 1.
This version is only available for Mac at the moment and is for developers to update their version of Cydia to make sure it runs fine on the iPhone OS 4.0