Previewed at WWDC, launching in the fall.
iOS 4.3 Beta Brings Software Option for Rotation Lock or Mute on iPad
One of the more controversial changes made with the release of iOS 4.2 late last year was a change in the functionality of the switch on the side of the iPad, moving it from a screen rotation lock to a mute switch as seen on the iPhone. Apple CEO Steve Jobs had even reportedly responded to a customer question by noting that the change was permanent and that it would not be a user-configurable option.
Apple appears to have had a change of heart, as today's iOS 4.3 beta appears to have added an option in the device's Settings application to allow users to customize the behavior of the switch.