Called from YPR, I said hello once and got no answer, then I hung up and they didn't call back.
I was told once by someone that did telemarketing in college that they are required to wait for the person they are calling to say hello twice before they proceed with whatever it is they are trying to sell or bug you about, I don't know if it is true but so far unless it is something legit, saying hello just once has worked for me. If it isn't a telemarketer they usually answer after the first hello.