Double sided mobile device - Yin and Yang

In a series of posts I have argued that it is a waste of space to use just one side of a mobile device. By thinking out load I have tried to find possible usages of such a device. You know that Apple's IPhone has a touch screen to interact with the device. Why not put a touch screen on the other side as well? Why would you do that you might think? Why would you not? I bet there are lots of situations where a double sided device would be more practical, more intuitive and easier to use. As a hypothesis, would it make sense to split up the most common usages and put them on each side? Like the Yin and Yang of a mobile device. I can think of several possible Yins and Yangs of a mobile device. Here are some of them:

• Yin - Content and applications. Yang - Communication.
• Yin - Geography. Location services, GPS, Navigation. Yang - The rest.
• Yin - Media and gaming. Yang - The rest.
• Yin - Health meters (such as pulse, blood pressure) Yang - The rest.
• Yin - Authentication. Fingerprint sensors. Security. Yang - The rest.
• Yin - Practical functions such as a flashlight or a mirror. Yang - The rest.

The question is: Is the single sided mobile device sufficient for all of the examples above? Is it more logical, more intuitive to use only one side? Are two sides only confusing for the user? I don't know since I haven't used a double sided one. An interesting aspect is if the two sides could be able to communicate with each other. How would that work? To be Xhausted...