Please someone tell me they have figured out how to do this!!

I want to receive calls via my deck speakers in my car. Just bought a new deck as well as the tomtom app (which I may or may not have paid for) and everything works so cuts out when tomtom talks. However, calls dont go through speakers which I was super choked about.

I DONT WANT TO USE AUX IN......just have an ON/OFF feature making it possible to hear calls over my car speakers.....exactly how the music and the tomtom can be heard over the speakers.