No connection to the mic, the only thing you can do with the AUX is play audio through it - music, traffic alerts from a GPS etc.
To make calls you have to have the bluetooth headset. Works very well too, managed to call a friend from 4000' over IOM a few weeks back and it was crystal clear for both of us!
ES
EDIT: forgot to mention, no matter what you're doing ATC transmissions will still be heard - you can set it so that it either plays at the same volume as the input, or so that radio transimissions always over ride whatever else is playing which is what i leave it set to.