The iPhone Dev Team has released the fifth beta of an untethered jailbreak for 4.2.1. As with all the others, this beta requires a 4.2 beta 3 SHSH on file (on your device), as well as the actual 4.2 beta 3 IPSW. The iPhone Dev Team said that a Windows version exists, but it is “painfully slow” and that they will delay the release until they can speed up the process. 
What’s new?
“The fifth beta is now available (testers ONLY please!). Bluetooth is now working (and any sandbox-related issues should be resolved too). Please do not pirate the 4.2b3 IPSW! Only those enrolled in the iPhone Developer program have legitimate access to that IPSW using these links (the links won’t work unless you’re a legit developer currently logged in).” (via iPhone-dev)
Wait, what? How do I use this?
Good question. In order to use this, you need to restore your device to a stock 4.2.1 IPSW, must have 4.2b3 SHSH on file (look at the top of Cydia, check to see 4.2b3 is there), and you must have the 4.2 b3 IPSW for your device. Please do not pirate this IPSW.
1. Select your 4.2.1 IPSW and let Redsn0w process the files.
2. Select “Install Cydia” and “Jailbreak Monte” — When you select “Jailbreak Monte,” it will ask for you to find the 4.2b3 IPSW.
3. Put your device into DFU mode, and let Redsn0w do the rest.
Enjoy your untethered jailbreak!
