Microsoft was recently awarded a patent for using a mobile phone to control a personal computer. It was filed back in 2005, and was only recently granted to the company.
The patent information below explains the function:
Systems and methods are described for using a mobile phone to control a computing device. In one implementation, a communication protocol stack is established that includes a wireless layer, such as a BLUETOOTH wireless protocol (IEEE Standard 802.15.1) stack, a communication layer that multiplexes the wireless layer into virtual channels, and an application adaptation layer by which the mobile phone controls and previews content from each of multiple applications on the computing device. The communication protocol stack dynamically maps mobile phone keys to computer keyboard messages for controlling the applications on the computing device. A data packet structure is established for communications between the mobile phone and the computing device via the communication protocol stack.
The patent describes wireless communication, such as Bluetooth, between devices as well as the ability to map out keys to the phone. This is no doubt much easier now with touchscreen smartphones. We've seen similar functions by Apple with smaller results, such as Apps that directly controls iTunes over wifi, or Apps that turn the iDevice into a trackpad over wifi. This patent makes for much more interesting results.