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After iOS 4.2, iPad's screen rotation lock switch, located on the upper-right edge of the device, will become a mute switch, similar to the mute switch on the iPhone.
According to Steve Jobs himself, who answered one of 9to5Mac's readers in an e-mail, the change is permanent, and -- although it's just a matter of a software tweak -- users won't be able to switch between the two functions.
This is a slight disappointment for users who are already accustomed to using this switch for locking the screen orientation on their iPad, but Apple is a company that likes having as little buttons as possible on its devices, and having one button doing two different things obviously wasn't an option.