If you don't answer, the person on the other end never even knows about the call. The call isn't connected to the telemarketing person until it is answered. Called a "predictive dialer". That is why sometimes no one is on the other end. None of the scum on the other end are available to take the call, so it just disconnects.
Annoying!! Called four times in less than two hours.... 2:41, 3:17, 3:55, 4:28. I don't answer any numbers I do not know!!! No messages left and they are now blocked.