I used to sing Private Number for my mobile's voicemail, but changed it a bit to:-

"I'm sorry you couldn't call me cos I'm at home, but if you could leave your name and message after the tone."

It's a bit boring now, though, cos it's just "Hi, this is Kat. Please leave a message." I'm thinking of changing it to "If you've got something important or interesting to say, the beep is your cue, if not hang up now!"