happend to me too.  I called back and it just rings.  I suspecion its the same people who have been blowing up my phone.  There is a home security system company that keeps calling from several different numbers.  I keep pressing the No. the messages says to press to be removed from their call list, but they just keep calling and calling and calling.  They have hung up on me 3 times as soon as I start to tell them how I have requested my number to be removed from their list.  I get about 1/3 into my spiel and they just hang up.  I can't wait to find out who these a-holes are.