Three calls in a row over 20 minutes while I was eating dinner. Didn't leave a message once. Seriously, people. If it's so important that you need to call that often in a short period of time, leave a message!
Not all those calling have a plan for an automatic answer, little is gained leaving messages. They need and are after a live voice most. If you can do it, don't even allow an automatic response and let the phone ring. That's one of the easiest ways to get pesky callers tired of messing with you.