What's the point of these random phone calls?

Just about every day I get one nonsense phone call. If I answer, it/they hang up; if I don't answer, there's no message. It isn't the same person because each time it's a different area code somewhere around the country. It can't be a telemarketer because they'd want to talk to me. But there must be a connection between the calls or else it wouldn't be the same thing every night. WTF is this?