I just got such a call and it was dead air. This was right after a call in which a machine asked my name.
(551) 226-6765 is a VOIP number in Jersey City, NJ (New York City area). The first call was from a listed Philadelphia phone number, which would not have a machine asking your name. It's possible that this person can spoof the Caller ID.
They called, no one there. A faint sound of electronics in the distance, I hung up. As a consumer I would like to buy software that reverse hacks these people and outs them to the police.