Telemarketer Dialer fishing for active numbers to then sell to clients for cold calling. It's the new thing in telemarketing. They set up a dialer and if someone answers, that number is put on the "gold list", if no one answers, it goes on the "blue list" (to be dialed again for at least 5 times). If number is disconnected or not answered by the 5th try, it goes on to the "black list". Best way to avoid is to block it with your iPhone.