I don't think it's really necessary to have it run in background. Just flip things around and it'd be fine. 😀 Make the app run in foreground because Phone, and Music can run in background.
If I were doing it I'd have it so you click the app and then it says speek freely, where you can speak a list of voice commands that can be spoken to you or visually seen. Then it can pull the music library or phone api's with call and play commands 😀