The iPhone Dev Team has just released Redsn0w 0.9.6b4 today which brings firs tproper jailbreak, with working Cydia and
MobileSubstrate for all iOS 4.2.1 devices. For those of you who don’t know, Redsn0w 0.9.6b4 is based on Geohot’s Limera1n bootrom exploit which has already pwned all
current iOS devices for life. The only problem is that it is a tethered jailbreak, which means
you will have to boot it into a “jailbroken state” on every reboot. This so called tethered or
semi-tethered jailbreak condition however only applies to the new devices like: iPhone 3GS
(new bootrom), iPhone 4, iPad, iPod touch 2G (MC Model), iPod touch 3G and the iPod touch
4G. Old devices like iPhone 3GS (old bootrom), iPhone 3G and iPod touch 2G (Non-MC Model) can be jailbroken-untethered right
now using this latest version of Redsn0w. So until and unless Comex of Spirit and
JailbreakMe fame comes up with another untethered hack for iOS 4.2.1, the jailbreak we get for the newer devices will be tethered (or
semi-tethered).