They called my cell today (Sunday) but never left a message.  When I try to call the number back I just get a busy signal.  I am wondering who this is and what they want.

Its a scammer calling from a spoofed number.  Stop answering calls from this number.

fund raising cold call

Same thing. The only reason I called back was that it was from my old neighborhood.

I just got the same call, but answered. It was a man and they were looking for the previous owner of my phone who I've been getting calls for since I got the phone 10 years ago. When I said the previous owner wasn't here and was about to explain myself, the man interrupted "Okay we'll try again later" and regardless of my WAIT NO. Obviously a nonsense call.