Is iPhone 5 call audio passed through Lightning connector?

Hi, my Dad's Honda has some kind of iPod integration; it provides a USB connector, and when you connect it to your iPod or iPhone then a small screen in the dashboard displays album art and song titles, etc. However, phone calls don't seem to work. The voice audio just comes through the iPhone's earpiece speaker instead of being piped to the car stereo like music is.

Is this just a limitation of the iPhone 5/Lightning connector, or are we doing something wrong?

Thanks!