Few moments ago, Apple pushed iOS 4.2 Gold Master into Developers Center. The newly released Redsn0w 0.9.6 has been confirmed to jailbreak iOS 4.2 GM on iPhone 4, iPhone 3GS, iPhone 3G, iPod touch 4G / 3G / 2G and iPad. So, if you have got your copy of iOS 4.2 GM, you will be able to jailbreak it using the instructions posted below.
Today Apple released to developers the GM seed for 4.2. Tinkerers will find that yesterday’s redsn0w jailbreaks today’s 4.2 GM seed, simply by pointing redsn0w at the 4.1 IPSW (rather than the 4.2 one). Right now it mostly only makes sense for JB app developers to do that because many apps (including Cydia itself) need to be updated for 4.2. However, if all you want to do is enable afc2 (to use iFunBox or other file browsers), or to tweak settings like Battery % and Homescreen wallpapers, then go for it (if you have valid paid access to the GM seed). Be sure to uncheck the Cydia box, though! Ultrasn0w unlockers should stay very far away from this!!
STEP 1: Download iOS 4.1 (required for jailbreak) and iOS 4.2 then connect your iOS device into your computer via USB and make sure that iTunes is not running.
STEP 2: Launch Redsn0w 0.9.6b2 and click Browse then point it to iOS 4.1 original firmware file NOT iOS 4.2.
STEP 3: Now select “Install Cydia” and hit the Next button to continue the process.
STEP 4: A prompt will appear to put the device in DFU mode. For this just follow the instructions appearing on the screen or hold Home + Power buttons at the same time for exactly 10 seconds and then release the power button while continuing to press home.
STEP 5: Congrats, now you can enjoy your jailbroken device.
Forgot to talk about the unlock, currently, there's no unlock for the new basebands of iOS 4.1 and iOS 4.2 but it's expected to be released just after the public release of iOS 4.2 in few days. We'll keep you updated whenever iOS 4.2 is available followed by Ultrasn0w unlock.
Download iOS 4.1 for iPhone, iPod touch
Download iOS 3.2.2 for iPad
Download iOS 4.2 GM for Developers
Download iTunes 10 for Windows and Mac
Download Redsn0w 0.9.6 for Windows and Mac