A person named “Pyrofer” has written a Java (J2ME) based software for Nokia 6230i (which can be ported to any other J2ME supporting mobile) that allows you to use it as a Bluetooth mouse for your laptop/PC.

Some of the existing features are:
Bluetooth connection, no cable
Standard Java code, simple to port to other phones
Selectable buttons on phone for mouse buttons
Normal or Flipped orientation for phone (right way or upside down)
Uses existing Nokia Sync software to transfer data

Other exiting features under development are:
Standard Bluetooth mouse HID for no driver install
Mouse over GPRS for PCs with net but no bluetooth
Display PC screen on Nokia phone