Here are two images showing the changes the iPhone and the iOS have had over the years.
Gadgetlove.com made a GIF of all the iPhones morphing into each other, showing how the iPhone has changed of the generations. One of the things that strikes me is even as the style of corners change and they have gotten taller, the iPhone has kept getting thinner.
7dayshop.com made an image showing how the iOS has changed, changes in app icons, the layout of the home screen, and the features from iPhone OS (iOS 1) to the current iOS 8. Some of the changes are subtle, the phone icon has always been green, and some are dramatic, such as adding 3rd party apps in iOS 2.