Stealth.
There are specialist CD's available with royalty free music especially for music on hold systems.
The two we supply and use ourselves (which you most welcome to call and have a demo of) are:
Music on Hold CD (Set 1)
• Atmospheric Music
• Classical Music
• Contemporary Music
Music on Hold CD (Set 2)
• Classical & Contemporary
• Easy Listening Music
Both have a dual set of tracks, one with voiceover (we apologise for keeping you waiting, blah, blah, blah) and one without. Keri, you're phone technicians need to be kicked in the butt or what they've said! The idea that classical music is safe due to the 'composer probably being dead' will hold no weight with the PRS as someone will undoubtedly hold the copyright to the music and it is them who would expect royalties. Would that mean I could now use Michael Jackson's music??

There are also CD players made to work with phone systems and these CD's. Nothing special, just a jack output and programmable tracks.
Hope this helps,
Paul