Sam Bashton has sent us details of a program he has created to adjust the volume of your PC while the telephone is in use. This could be used to play music while you are not on the phone and turn it down when you are:
autovol is a program which automatically adjusts the volume of a computer whenever telephones are in use. autovol caters for multiple telephones, which makes it useful in an office environment where many phones may be within earshot of the music playing device. At present autovol only supports telephone devices which are connected to an Asterisk server.