As we told before that iOS 4.2.1 can be jailbreaked on new bootrooms and it will be tethered. Means every time you connect you boot up you will have to connect to your pc and boot up via redsn0w.
But it seems no need to do it from now onwards because a member of chronic dev-team said that:
He got a backup plan for the untethered JB working. And he will be showing up a video soon.
We think it will only work for those who had saved their SHSH saved for 4.2b3.
But he gave another tweet that @Comex is also working on the untether jailbreak. The one @Musclenerd have got is just a backup plan.
Looks like we will be having a untethered jailbreak really soon for the new bootrooms which are MC models. And the jailbreak may not need the SHSH for 4.2b3 because many people who just bought their iDevices will be on 4.2.1 and they won’t have their SHSH saved.