Most of these companies use the same name lists, and if you are a complete time waster they will mark it against your name and reduce the chances of being called.
A funny one i heard about or read somewhere,
A guy receives a call at home from a tele sales rep. The guy is polite and asks the callers name, and a few other pleasantries are exchanged. Eventually the guy asks for the Reps home number. "Sir I cannot give you my number" the rep replies.
"Why" asks the guy, "Is it because you don't want people phoning you and annoying the crap out of you at home?" and hangs up.
A.K.A - br1an