This was an "abandoned" or "dead air" call. "Abandoned" calls (telemarketing calls that are not connected to a live representative within 2 seconds after you answered; characterized by "dead air") from any source - including "legitimate" charities and their telemarketing agents - should be reported as such to the FCC. Go to http://esupport.fcc.gov/complaints.htm to do this.
I received a call from this number today, even though I have AT&T's "privacy manager" on that line and am also on the "Do Not Call" list. It was the one asking if I (or anyone I know) is overweight.