They call, won't leave a message.  When we answer, they hang up!

Yup. Same thing.  I answer and since there is a pause, I hang up.  Must be an unsolicited sales call. Not answering again.

call me, left no message

Same as the previous posts, except I called back once and it went to a voicemail message saying, "you have reached the fundraising office, we can't take your call right now...".  I didn't leave a message.

They've called me as well.  Same thing, no message and hang up when I answer.  I tried calling back, but I just get a busy signal.