I let the house phone ring to the answer machine then they either leave a message or not,if a message is left then I can decide to reply or not.Biggest part of the time no message is left.On my mobile I only answer that if it's a number known in it's memory and everyone I know generally uses text messaging.
I used to do that .. what I got was messages from various medical establishments for people that don't live here. Oh and occasionally 'Ethel' (no idea of the name, sounded about 1000 years old) asking if 'Janice' would be picking her up today.
The phone is no longer even plugged in.. that solved that nicely.
I found my phone bill was mostly made up of calling everyone back, and speaking to their answerphones, as they also had the same idea
My physical landlines go into Asterisk, where they go around a really annoying IVR, with only a single, not mentioned path to actually ring my phones (although a few numbers are in a bypass group).
My VoIP lines come into the same Asterisk, by straight through to the phones, and in 15yrs of having the same VoIP numbers, I have never, ever had a marketing call on any of them. My physical lines are both TPS registered, and get around 7 a day each, looking at the phone logs.