The callers are checking/verifying phone numbers. When you answer, they log it as a legitmate phone number. They then either start their scam calls or they sell your phone number to whoever is buying... or they do both. Either way, the best way to stop scammers and telemarketers is to STOP ANSWERING YOUR PHONE when you don't recognize the number. Anyone who has legitmate business with you and has any reason to call you will leave a message, in which they identify themselves and explain why they called, as well as leave a call-back number.
Got a call at 5:10 PM Eastern Time, I'm in Michigan.
Recorded message about a new kind of home security system, said press 1 to speak to repreentative, press 2 to be removed.