Symantec warns of a worm for Series 60 mobile phones that transmits itself through Bluetooth. It's just a proof-of-concept (doesn't do any damage), but it's a scary concept:
The worm spreads as a .SIS file, which is automatically installed into the "APPS" directory when the receiver accepts the transmission. Upon execution, it will display a message then copy itself to a directory that is not visible by default. The worm runs from this directory whenever the phone is rebooted, so it continues to work even if the files are deleted from the APPS directory.