When I connect my Zumo 220 motorcycle GPS to my Cardo Scala Rider G4 headset, it stops the connection from my Droid X phone, and I can't make calls.
I then paired the Zumo 220 to my Sony radio. The audio only plays if I called BT Cell Phone and not BT Audio. This leads me to think the Zumo 220 is connecting as a cell phone, and not just a bluetooth audio device. My headset can only pair to one cell phone at a time, which makes sense.
The zumo 220 shouldn't be connecting like a Zumo 550 since only the latter supports a cell phone to be connected to it along with a headset.
If I am correct, Garmin should change it so it connects as a BT Audio device.