I have a 05 tour deluxe and was thinking the same thing. I looked around and found a system called Autocom The website is being rebuilt at the present time. You can found Bob's BMW motorcycle website or call Top Gear accessories in New York at (888)851-4327 and get a catalog.
The system mounts under the seat then you can hook up music,cell phone,radar units and bike to bike. When you talk to your passenger the music will cut the volume in half or when the rings it cuts out. I have had the system for about a year and very happy.