I think this is a computer that calls people with the intent of having it ring once so you will see a missed call on your cell phone or caller ID and call them back only to hear a recorded message. I guess in their sick mind it is a way to avoid the do not call registry or something. When one calls back, it gives them confirmation that it is a good number. Probably then sell your number to a million other telemarketers as "known good" numbers....
I called them back on an anonymous phone. They said that I was going to get a $100 reward card. But I had to stay on the line. So I did and some foreigner picked up and said hello. I just made cave man noises for a minute as he kept saying hello. Then I hung up.