This caller has rung my phone several times and left no message when requested

This number showed on my call display a couple of times, and each time I answered, it was just dead air. It does not sound like there's any connection on the other end. After a while, there's a soft click, and it actually does disconnect.
Calling the number back gets a "number not in service" recording from AT&T.
I'm in Ontario, Canada.
Call log so far:
May 28 2012 8:52PM
May 29 2012 12:09PM

Same as Greg B. am from Ontario as well
Dead air then click, Callback goes to At&T
1:24 June 19 2012

I keep getting calls from this number as well.  When I asked the rep today to pass me to a supervisor, he wouldn't and assured me that I wouldn't be getting these calls again....this after telling me they do not have a 'do not call list'!!  After requesting to speak to his supervisor 3 times...he just hung up.  Sigh.  How do I stop these calls?

This caller has rung my phone several times and left no message when requested