I never answer the phone if the zip code is outside my area if I don't know the number. 90% of the time they don't leave a message. Lately I've been getting a call every day from a different state. No message, just kind of fun seeing what state they are calling from. We have been joking about it, but I sometimes wonder what their scam is.
Back before smart phones and being able to see the number calling I heard on the radio that a good way to fight back on unwanted phone calls was to keep them on the line as long as possible. Talk to them, sound interested and then tell them to hold on a minute. Then put the phone down and see how long they wait before hanging up. I tried it a few times and they where always gone when I checked the phone again after doing whatever I was doing. I don't know how effective it was, but I don't remember getting anymore calls from them.
Eddie