Those looking for the iOS 4.2.1 Untethered Jailbreak from Comex before the 2010 Christmas are little bit disappointed to learn that this is not going to happen before the Christmas. Comex had earlier expressed hope that the iOS 4.2.1 Untethered Jailbreak should be available by the Christmas.
All the present iOS 4.2.1 jailbreaks are tethered jailbreaks and this tethered jailbrak includes the jailbrak for earlier iPhone 3GS , iPhone 4, iPhone Touch 4G, 3G and 2G.
A tethered jailbreak requires that you need to connect it to computer again in case if your turn off for any reason and you need to turn it on. This is inconvinient to many users and hence the demand for the untethered jailbreak.
Here is what comext says on his twitter
@comex: I think I’m going to miss my Christmas deadline
We however have a back up plan for the untethered jailbreak on iOS 4.2.1 iPod Touch 4G from MuscleNerd who demonstrated it. This works differently that Comex exploit and needs that 4.2b3 SHSH saved.
Stay tuned as we keep looking at more iPhone jailbreaks coming in future.