Any tech writer could scrawl for days about the importance of the iPhone. But let's focus on how, despite being the most revolutionary phone (or, hell, gadget in general) of the past 20 years, it was also stunningly simple, especially at launch. In 2007, the iPhone did things no other phone did, and a lot of its differences were subtractions. No apps, not for a whole year. No 3G, which, in these days of 4G, we forget was such a big deal in 2007. No removable battery, a decision that inspired derision and outrage from the tech press. Only a single function button--home. The iPhone is complex in lots of ways--its pioneering use of multitouch gestures, accelerometers, and software-based keyboard were all new ideas, and are now ubiquitous--but at its core, using it was simple and easy to understand.