Got a call.  Didn't answer.  They left no message.  The do not call listing is a joke.

Same.

This number has called 5 times today and 4 times yesterday.  When I answer, there is no one there.  If you call the number back, it's a nonworking number.  What would be the purpose of never speaking or even leaving a message for someone?  No message is conveyed at all.  It's only a persistent annoyance.  Call says it comes from Casa Grande, AZ ...

Yes.  When you answer, they keep saying "hello" ... "hello" ... and even will say "Of course" as if they are actually having a conversation with you.  I suppose they are being monitored by a supervisor who is pushing them to have a conversation, but in actuality no one ever lets you know why they are calling.  Very harassing and non-stop.  Several calls a day.