Funny voicemails are a great way to spice up your messages. You could say something like hello? Hello? I can't hear you. Please speak up, it's a bad connection. If you pause just long enough, the people will think that you really answered. You could remind the callers that you don't want to buy siding, furniture, a car, dentures, or even a broom. Remind callers that they are talking to a machine.
. Let them know that you're practicing your ESP abilities, and will think about calling them back. More funny ideas are at http://www.buzzle.com/articles/funny-voice-mail-messages.html.