Update! The adapter bluetooth allows calls to be taken, no matter which source is in use. That means I both my phones are available to be answered (though not at the same time). I was listening to the radio when a call came in through the adapters bluetooth. That was the final test, because I thought stereo had to be in adapter/USB mode to receive calls. The system simply switches. Even though the car already had bluetooth, it was limited to one phone, and handle calls only. Not music playback