Hey folks as we told you before that Untethered Jailbreak for iOS4.2.1 is out and you grab one from here. This release of Greenpois0n is only for MAC till now and many of you want to try it out, but you cannot try it due to baseband updating thing.
The solution for this was posted by @MuscleNerd that:
The Dev-Team will update the PWNAGE tool which is only for MAC and the reason to update is that you can preserve your baseband and update to iOS4.2.1. Specially for people on iPhone4. Although we got Custom iOS4.2.1 for iPhone4 which preserves the baseband and let you update to iOS4.2.1 without any errors. But it is good to wait for the original PWNAGE Tool be updated.As it will be based on Greenpois0n exploit so it will be also for all the iDevices except iPhone3G. We will post up as soon as we hear any thing new on it.