Hang up if you know someone is on the phone or want to use phone
Many times, I was on the phone up stairs, my hu*****and was trying to dial down stairs, I will tell him to stop or I stop my conversion...
It worked well, but since you are really apart, you should tell your son to make sure you are not on the phone conversion. In another hand, you need to do the same way...
My point here -- Talk firmly and let him know your thought and let him respect you...
Prepare worse way: Looking for new one!