Make what you will of the various reports about using hands free is a distraction. Everyones abilities are different and some would be capable of multi-tasking in a driving situation, while others have enough trouble just operating the door handles.
While the implication that having a telephone conversation while driving requires a perceptualisation of the conversation, is this any different from listening to a talk show on the radio or even a audible book.
I have no problem listening or taking part in some conversations either with passengers or on the hands free phone, radio or an audible book which are ideal for long journeys. I know when I have to stop listening or talking when the road/traffic conditions require attention. This takes priority.
When I got my newish slightly smarter car, there where far more distractions from all the warnings and information being presented while driving than any type of audible conversations. Eventually I got used to them and can now put them to the rear of my mind while I concentrate on the driving.