I just got a call from Mary Stewart (according to caller ID). Did not leave a message. I called the number back and received an immediate message "This caller has a voice mail box that is full". The only reason I tried to call back is that I am selling an RV and thought it was from an interested party.... egg is on my face. Now I know it is a telemarketer scam.
Keep your answering machine turned off and use telephones that display the number calling you. Don't answer the phone manually if you don't recognize the caller. If you are not at home when you get calls, you can look at your phone later to see if someone important or known to you has called. If your answering machine answers your phone - You get onto a list!!!
The concept of "wardialing" makes irrelevant being on any list. A program can and will cycle through valid, invalid, and hostile numbers alike, in an area code and exchange. "lists" can be helpful, but are not important to them. If so, the sh*theads from Scam Services would remove from their "list" "hostile" numbers. The degree of grief that has come from one of my phones to them, including toying with them on calls for prolonged periods of time before busting their agates and telling them to perform an impossible act SHOULD have marked that number as "hostile - waste of time -", but they don't. Instead, I get the routine calls from some single-digit IQ having criminal that's bound to get mad after being toyed with.
Likely the only thing to stop them will be turning their "office" into the opening scene for a CSI episode. Not that anyone would really miss them though...