iOS 4.2 Direct Download Links
You can download iOS 4.2 directly from iTunes 10.1, but if you’d prefer to use a direct download link, here they are from Apple:
iOS 4.2.1 Direct Download
These are direct download links from Apple’s servers. It’s best to right-click on the file and then “Save As” to prevent any problems downloading the IPSW.
iOS 4.2.1 IPSW for iPad:
iOS 4.2.1 IPSW for iPhone:
iOS 4.2.1 IPSW for iPod touch:
iOS 4.2 IPSW for Apple TV:
The official release of iOS 4.2 is actually iOS 4.2.1 with build 8C148, which is the same as the recent 4.2.1 GM. The only exception is the Apple TV update, which is 8C150.