Caller ID is just the number.  They leave no message.

I call back during business hours (using *67 to block my number).  I hear the following, "Welcome to Verizon Wireless.  The number you dialed has been changed, disconnected, or is no longer in service.  If you feel you have reached this recording in error, please, check the number and try your call again.  Announcement 2 switch 2 8 dash 1."

So you can't call them back.  Smells like a SCAM.