You Can Already Jailbreak iOS 4.2 GM If You Wish
November 2, 2010
Now that you have installed iOS 4.2 GM on all your iDevices, may we interest you in some jailbreak fun? Yes, the latest version of the redsn0w jailbreak tool, released last weekend, can already jailbreak Apple's latest version of iOS.
It's very straightforward. Once you're running iOS 4.2 on your iDevice, you can jailbreak it directly using Redsn0w (available here). The only trick consists of pointing Redsn0w to an iOS 4.1 firmware file when requested (you can find that here).
Of course, there is a little catch. That is, Cydia as well as most of your jailbreak apps are simply not ready to run on iOS 4.2 yet, so there won't be much you can do. The Dev-Team even recommends you uncheck the Cydia installation box in Redsn0w altogether. If all you care about is accessing the file system and messing around with it, that will do the trick.
Of course, for now, don't update your iPhone if you care about unlocking it.