On his twitter account Comex has just posted that he may not be able to release the untethered jailbreak for iPhone 4, iPhone 3GS New bootrom and iPod Touch 4G by Christmas.
Comex’s jailbreak is based on Limera1n exploit and it needs some kernal hack treatment to make it untethered.
Though the iPhone Dev Team is also working on “Plan B” untethered jailbreak, but Comex hack is more extensible and should not require access to the developer only 4.2b3 IPSW.
Comex:I think I’m going to miss my Christmas deadline…
You might also like to check out these posts to get an idea of iPhone Dev Team’s progress: