If you answer a call and no one is there, you were called by an "auto-dialer." The Federal Communications Commission (FCC) requires that calls made with an autodialer "get live" within about 3-5 seconds. If they don't do that, it's a dropped call and you can report it at the Federal Communications Commission's web site. The Federal Trade Commission (FTC) regulates the DO NOT CALL list, but the FCC regulates "war dialing" (testing to see if you have a fax) or "abandoned calls."