From 2002 to 2007, I used to walk around everywhere with a little spiral notebook in my back pocket and a pencil sticking out of my hair. This was how I managed my schedule, to-do list, and (as a college student) the doodles I made of my professors.
Then the iPhone came out. Suddenly, the slew of apps in my pocket made it possible to do and keep track of much more than my little notebook used to allow me to do.