I read this on the message board for one of the personal coaching programs I'm involved in, and thought it was particularly useful:

On voicemail greetings, people tend to record a message along the lines of "Hi, this is Tom, I'm sorry I missed your call, please leave me a message and I'll return your call...."

Generally, that's functional, and lets you know someone wants to talk to you.

If you changed your greeting to the following, you can be sure you only return calls to people who follow the instructions in the voicemail, and avoid playing silly phone tag with people for what may be an unimportant call.... People will leave the right message if they really need to speak to you and if it is urgent:

"Hi, this is Tom. I'm sorry I missed your call. Please let me know why you called, so I can get to work on it before I call you back. Thank you!"