Remember your portable paper-based Day Runner organizer and calendar? We carried it everywhere. Many of us switched to the handheld Palm Pilot, reinforcing the notion that a calendar only works when it's mobile and always close to us. Then came the iPhone with its built-in Calendar app. Not only could it sync with the desktop calendar but alert us to meetings and other events. If you think you can live without it, just add up how many times you look at the Calendar app per day.