9-2-16, 11:07am. Diverted by a service I subscribe to that intercepts robo-dialed calls (rhymes with SoNoHobo). The number belongs to Patrick 24-HR Heating and Air, but caller ID said "Unavailable."
Over the past month or so I have received several calls from the phone numbers of legitimate businesses but with no true caller ID, and I suspect this pattern to be a result of spammers and scammers possibly inadvertently spoofing a working number.
I called one of the earlier ones back, explained that I had gotten a call from that number, but since she was not able to find anyone in the office who had dialed my number, she said it must have been a mis-dial.
I have never gotten a second call from any of these legitimate numbers, which seems to support the spoofing theory.