I assume this is a type of SPAM call center.  We receive 5-10 calls per day on our 5 lines at my business, from the 347 area code, and always a rotating number.  There is no one there, just dead silence.  It is very annoying, and after normal business hours, the call leaves a 10 second blank voice mail on our system each time.  I wish I could block an entire 347 area code from our phone system.