yeah i saw this app too, looks like a must-buy to me. I just hope that it will be able to work in the background and maybe be activated by some sort of finger gesture or something.
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