How-To: Use a HTC Touch Diamond or Touch Pro as a mouse replacement
GRemote requires a connection with the computer (WiFi, bluetooth or USB) and the computer must be running Windows or Linux. Installation is a somewhat involved process and the application is very much in beta, but it should generally work as advertised with the abovementioned devices and may soon also work with other, similar devices (such as the Samsung OMNIA).
iPhone users can turn to "Air Mouse" for similar functionality (available on the Apple App Store for $5.99).
source: xda-developers via jkOnTheRun