Today greenpois0n RC5 was officially released, it makes untethered jailbreak for iOS 4.2.1 why with Mac OS X. Unfortunately Chronic Dev Team failed to implement a system of activation of the terminals, so people who do not have the telephone operator's card on which the iPhone is blocked do not have access to the system. Well, there is a solution for this problem, a fairly simple one by the way, jailbreak with redsn0w. redsn0w makes a tethered jailbreak for iOS 4.2.1, but it also activates the terminal and greenpois0n RC5 can be run over the jailbreak made by redsn0w without the slightest problem. You have a tutorial for tethered jailbreak with redsn0w on iOS 4.2.1 here, tutorial for untethered jailbreak with greenpois0n RC5 you have here.
For the problem with Cydia, the solution is just as simple, use the same tethered jailbreak tutorial for iOS 4.2.1, but do not select to jailbreak but only select Install Cydia and after redsn0w finishes its process you will have a terminal with untethered jailbreak and Cydia installed.
For those having trouble getting Cydia via the GP Loader, just let redsn0w install it (don't choose the Monte option)
(The reason that works is tethered RS doesn't touch boot sequence at all, but GP does. They stay out of each others way)
