Calls are coming to my office,  where I have multiple lines.      Calls must be generated by a computer,  because all three lines eventually start to ring at the same time,   especially when I don't answer (because from what I can see on my caller ID it is likely a "SCAM" call  - - since most of my clients are local).    So when I don't answer,  the lines continue to ring,  so that eventually all three lines are ringing at the same time.