Car radio that will mix sound inputs and play them at the same time?

Is there a car radio that will mix sound inputs and play them at the
same time?

AFAICT, both the Mazda 2 that I had and the current Honda Jazz/Fit and
maybe any other car I've driven lately only allowed one input to the
"radio" at a time.

So if I wanted to play the music on my Flashdrive, I couldn't get
notices from Google Maps where to turn, etc. (Since google maps is not
in the rental car, or any car I'll buy. It's only on the phone.)

And if I wanted to listen to local radio, via the radio built into the
radio, I couldn't get notices from Google Maps where to turn, etc.

If I depend on the phone only, it's nowhere near loud enough to be heard
over the music or talk. When I tried this at home, I often don't
hear the navigation instructions at all, even though they are set on
loud, and if I hear a voice, I certainly can't understand what it said.


The phone can be connected by bluetooth or probably AUX. I presume that
won't make any difference.

Is there a car radio that will mix sound inputs and play them at the
same time?