Callers who don't leave messages don't deserve the time to call them back. I've saved this number to my phone under "scam" so I can ignore them if they call again - unless of course they leave a message.
Simply another "missed" call, since I won't pick up an unrecognized number. If the caller wants to talk to me, a message will be left. When same number calls repeatedly, it is then added to the blocked caller list.