Caller ID says "V" followed by 19 digits. They leave no message.
I call back after hours (using *67 to block my number). I hear the following, "Sorry, the number you have reached is not in service. Please, check the number and dial again." There is about 10 seconds of a busy signal. Then about a minute of silence. Finally, there is an extended busy signal. I am convinced that everything before the last busy signal is their outgoing message.
So they spoof their caller ID. They fake a disconnevted phone, and they can't be called back. Smells like a SCAM.