Leaves no message like others have stated.
Spam calls if you call back. Received 5 calls back in one day, after calling back once.
When you call it states no representative is available press 5 to remove from call list.
The five option does work kind of, the number does stop calling you. However a number from CO, USA starts calling you and it is the same message if you call them back. That number is (720) 639-8033.
My phone shows the current number is being called from Port Huron, MI
TraceLookup says the company is:
Cellco Partnership Dba Verizon Wireless - Mi
(Will say other sources show other companies, but overall it comes up as a scam caller.)