iPhone hacker of Chronic Dev-Team, Pod2g has confirmed that the updated GreenPois0n tool will untether jailbreak iPhone 4, 3GS, iPod touch 4G and iPad running iOS 4.2.1 OOB. It does not require SHSH blobs for iOS 4.2b3.
About the 4.2.1. OOB jailbreak : it will be for all devices supported by gp at that time.
Last week another exploit for untethered jailbreak for iPhone, iPod touch, iPad running on iOS 4.2.1 has been discovered by SHAtter jailbreak exploit fame pod2g and it is expected that it will be used in new tool to jailbreak iOS 4.3 or later. Few days back we have also seen a teaser video of untethered iOS 4.2.1 jailbreak running on iPhone 4 which is posted by Joshu Hill, the member of Chronic Dev Team.
However, the team is providing any exact ETA for the release of the untethered jailbreak but they are claiming that they have almost completed it. It is also rumored that GreenPoison will be sporting custom boot logos and verbose boot.