The problem with voice mail is this: as you're leaving a voice mail for someone and you suddenly slip and say something really tawdry, you can't take it back--it's there forever. This is the subject of occasional HI-larious subplots in various movies. But the sobering fact is that this can happen in real life as well.
So, if you're going to leave a voice mail, think it through before you start babbling incessantly. There is no do-over.