It would be similar to the kenwood, you would see both devices on the screen and it would show in green which it is connected to. You can press a button to disconnect it from that phone and then press the other phone showing on the screen aswell and then it will connect to that one
Sounds like only one device is usable at a time then? In modern head units you can have both connected so that you can have one playing music and then use another to make a call. It will pause the music and resume playing when call from the other device has finished.