I have an iPhone 4. I love to use it. I like how it feels and how it looks. I most of all appreciate the user interface. It has a lot of sensors and tools that makes interaction with it more novel and useful. It has a multi-axis accelerometer for motion control, a moisture sensor for warranty assessment, a proximity sensor for saving power when talking, a microphone, 2 cameras, a gyroscopic sensor for motion control, a compass, light sensors, a GPS, a vibration device, and an illumination sensor for the camera.
I began to think, what else could my possibly have to make the phone more novel and useful. This short video presents some ideas of how phones or other interactive devices could give feedback in new and interesting ways: