I answer, they hang up also.

CID:  Out of area

rec'd a call at 10am, answered - i answered and no one there or they weren't talking.   BLOCKING NOW!

Caller hangs up upon answering

Called 9/2/2013 and somehow triggered call waiting on my phone, which I never knew I had.  I was on a long distance call and chose not to answer as I didn't recognize the number nor know anyone in the SFO area, especially anyone who would call me on Labor Day.

Weird.

I've been getting these call for several years.
This what I've found to be pretty effective.
I made a list of spam callers phone numbers and when one of them call, I answer with
AN INDIAN ACCENT AND SAY HELLO, HELLO, HELLO, AND I DO NOT INGAGE IN CONVERSATION WITH THEM. This drives them crazy and they hang up.
Mission accomplished! Then they put me on their DO NOT CALL LIST. !!!! I win.  

Now, those call have dropped off a lot.
It works for me, Try it You'll like the results.
9/6/13