I don't know who they are.  But I got an out-of-area call showing this number - caller ID says "Michigan".  I did not answer; they didn't leave a message.  My guess: likely spam.  I don't recognize the number, wasn't expecting it, and it came to a phone for which I don't give the number out except to friends mostly.

Yup. same here. This has got to be about the 50th call I've gotten in past 30 days alone from all sorts of numbers who never ever leave messages.  Idjits need to get a real job.