We are still not sure what version number is Apple following for iOS 4.2 but from the direct firmware links it looks that this one is iOS 4.2.1. If you are still waiting for iTunes to prompt for new software update message then use below direct links to download iOS 4.2 for your idevice straight from Apple Server.
Direct Download Links for iOS 4.2.1
Dont update to iOS 4.2.1/4.2 if you want to jailbreak & unlock your iPhone, iPod Touch & iPad.
Stay tuned with us for more on iOS 4.2.1 jailbreaking & unlocking.