These telemarketer clowns call using multiple phones at a time, they dial two or three people, and that's why it takes them a moment to actually answer if you happen to pick up (I saw this trick used by real estate salespeople).
About 1/2 the time they will ask for a fictitious  person (always Mike Smith in my calls), then when you say they have the wrong number, they apologize and start talking about refinancing your mortgage. The other 1/2, they ask for you by name and start the refi pitch.