Apple has posted a new video-based guided tour of the iPhone. The tour, which is roughly 20 minutes in length, explains the most of the basic functions of the device, and how to use them. Of note, the tour gives explanations for all of the iPhone’s external buttons and ports, including the silent/ringer switch (found on the side with the volume up/down buttons), and sleep/wake button (found on the top of the device). The video also…