According to Comex, the infamous iPhone hacker behind tools like Spirit, JailbreakMe and Frash, all those who have SHSH blobs saved for iOS 4.1 or earlier will be able to enjoy untethered iOS 4.2 jailbreak on their devices. Though this hack is not ready at the moment but it'll be available with official iOS 4.2 jailbreak tools like Redsn0w, PwnageTool and Sn0wbreeze.
Update via Comex:
You can easily save iOS 4.0, 4.0.1, 4.0.2, 4.1, 4.2 SHSH Blobs with TinyUmbrella. TinyUmbrella is available for both Windows and Mac users. You can find our step-by-step guide here to save iOS 4.1 SHSH blobs of iPhone 4, 3GS, 3G, iPod Touch 4G, 3G, 2G, Apple TV and iPad with TinyUmbrella. Once you are done with saving SHSH blobs, you will be able to do an untethered iOS 4.2 jailbreak on your device in future.
For those who don't know, Apple will seed iOS 4.2 final version in November this year and iPhone Dev-Team have promised to release Ultrasn0w unlock for iPhone 3GS/3G on iOS 4.1/4.2 within a day or 2 after its release.Contact Us for News Tips, Corrections and Feedback