Answer: There are many wise things to do in a situation like this. If the reason why you want to phone your friend is really urgent, then it is advisable YOU PULL OFF FROM THE ROAD AND GIVE THEM A CALL. It is not advisable to call and drive as this might cause distraction which is not only dangerous for the caller but for other road users as well.
If the reason for the call is not urgent, then it is advisable to wait till you reach your destination before making that call.