My research on robo calls is that the auto dialer dials number faster than their human staff can answer. But by answering you told them that they had a "live" number.

Called 11/5/14, 12:21 pm PST.  Caller ID showed "Unknown Name" and this number. whitepages.com shows as VoiP from Pasadena CA, intelius.com shows as cell home also from Pasaden CA.  My phone answered by Sentry robo call blocker. No message left.

Same miserable old scammers with a new number.  You block one, they come right back with another one.  It never ends.