Alright, a friend of mine has recently upgraded to iOS 4.0 on his iPhone 3G. Now, he doesn't have multitasking, and would like it. I myself have a 3GS and am on 3.1.3jailbroken. So, I went and got the iOS4 ipsw from the web, downloaded it, got Redsn0w 0.9.5, but I'm wondering what to do next? tl;dr, is it possible to jailbreak a device that is already on 4.0? If so, how? I have a Mac, if that helps.