This might be a variation of a scam from South Africa. It uses 024-5698 and the one listed on 800 notes is using area code 803 (South Carolina). I got the 803 one and 3 days later got this one with 856.

Caller ID shows "Name Not Found", exchange of 024 is clearly fake. I answered anyway to see if I could get some information, after several seconds of silence there was a loud "squawk" but no voice, so I hung up.

Caller ID read "New Jersey"
I answered the phone and a "woman" named Nicole said "Hi, we will be in your area and we are giving away free cell phones so you can replace your land line.  Are you the owner of the house?"
Me:  "Is this a real person or a computer generated voice?"
Nicole: *laugh* "No, of course I'm real."
Me: "What color is the sky?"
Nicole: "I'm sorry, I can't give out personal information."
Me: "What color is the grass?"
Nicole: "I'm sorry, my supervisor wouldn't like it if I gave out such personal information."
Obviously a computer generated voice trying to make you think you are talking to a real person.  In my opinion that alone is enough reason to call this a scam.

They call several times a week. I don't pick up but they don't leave a message either.

I got a call from the same number but 703 area code.  No message left...