On January 20, 2010, the US Patent & Trademark Office published a patent application from Apple that reveals one of the next chapters for Apple's Magic Mouse. Apple is working on combining the Magic Mouse's touch surface with either an OLED or specialized display surface made of collimated optical glass that contains a unique magnifying capability.
The display will be able to display a calculator when in use with Apple's Numbers app or be able to magnify text when using Apple's Pages app. The interface could be used for other applications in the future, and an iPhone keypad isn't out of the question.
Apple puts in summary that
"While sophisticated devices such as the iPhone provide significant information to a user regarding use of the device as a controller. For more common and basic input devices, such as keyboards, mice, trackpads, tablets, etc., functionality available through the input device is not usually conveyed through the input device, but, if at all, through the user interface on the system to which inputs are provided. As a result, it is not always apparent to the user which input should be used to access particular application functions."