Apple has released iOS 4.2 beta 2 (build 8C5101c) and iOS SDK 4.2 to developers of iOS Dev Center.It is available for iPhone, iPad and iPod Touch.
iH8sn0w has published iOS 4.2 Beta 2 keys for iPhone 3GS indicating that it will be possible to jailbreak iOS 4.2 using SHAtter.
According to the iOS 4.2 release notes, these are requirements to test the new wireless printing feature AirPrint:
* A printer that supports AirPrint, running the latest available firmware
* A printer shared through a Mac running Mac OS X 10.6.5 beta, available on the iOS developer page
* A printer shared through a PC running iTunes 10.1 beta, available on the iOS developer page
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