Tricks of the Trade has a great tip for those who still leave voicemail messages.
Caller - When leaving a voicemail, it's considerate to provide your number or other contact information at the beginning of the message, rather than at the end. That way, if the person wasn't able to get the info written down or memorized on the first pass, they don't have to re-listen to the entire message to hear it a second listen.
I couldn't agree more! It would be even better if people would text instead of leaving a voicemail.