Nadeem has rolled out what is touted to be the first PwnageTool custom bundle that will jailbreak iOS 4.2.1 on iPhone 4, and it has been assumed to run just fine so far. The Readme file that comes with this bundle claims it can be used with PwnageTool 4.1.3 in order to develop a custom iPSW for iOS 4.2.1 so that it can preserve the iPhone 4′s Baseband while booting untethered and jailbroken. You can give the download a go here if you’re interested, and here’s what the bundle description says :-
This is an untethered bundle for use with PwnageTool to create custom iPSW preserving the Baseband and also booting untethered and Jailbroken.DO NOT TICK THE ACTIVATE IPHONE OPTION WHILE MAKING THE IPSW IN PWNAGETOOL.This bundle supports legit activation only (too lazy to make the patch).> copy the .bundle files to PwnageTool.app/Content/Resources/FirmwareBundles/> copy info.plist goes inside PwnageTool.app/Content/Resources/CustomPackages/CydiaInstaller.bundle/ (IMPORTANT IF YOU WANT CYDIA IN YOUR IPSW )Props to pod2g, chronic-devs,iphone-dev and everyone. Limiting tools for the sake of exclusivity is no good.