Because e-mail and voice-mail have been used for so many things for so long, it will take some practice to wean ourselves off these sub-optimal technologies, and they will continue to be available for communications with those outside the company.
I’m afraid I have no brilliant advice. Your time is a zero-sum game, and only you can decide how to slice it up.
No matter how much you try, you can never think of all the things that someone might do or not do to surprise you. And, even with the best intent, sometimes people do things you don’t want them to do.