the phone: Legal way to definitely stop the calls - answer with "Please put me on your NO CALL LIST." They have to do it, and it has completely eliminated phone sales calls for me.
the door: Don't answer it if you don't know the person at your door. Have a way to view their face, so you can choose for whom you open your door. Put up a sign next to your doorbell, "Do not disturb." Tell your friends why it is there.