Here's a trick that's good to know.
When you pick up the phone and say "hello" and no one answers, it's often because it's an auto-dialer for some big faceless corporation. If you say "hello" again you will soon hear the greetings returned by a poor telephone salesperson... and of course in the backround you will hear all of the rest of their co-workers, jammed into the room with them like chickens on a semi.
So, here's what I do. I say hello one time... ONE TIME, that's all you get. And then I hang up the phone. TAKE THAT! JUSTICE! JUUUUUUSTIIIIIIIICE!
Um. If you're my friend, though, you should just call back if I hang up on you.