Music has been one of the first areas where this become a reality.
With iRig you may turn you iPhone or iPad in a music studio. Just select the software modeled amp and effects and you are ready.
You can turn your iPhone in a POS accepting credit card with Square.
You can measure distances using echoes (here).
There are dozens of application to check your heart rate using the mobile phone camera and flash, and one of your fingers.
Your phone can be used as a baby monitor, or a spy device if you like.
And these are just the applications I can remember right now. There are hundreds!
As I was writing in my previous post I think this is definitely a new area we should look at for innovation in mobile.
It shows how the environment around you can be connected to your mobile phones in ways that we could not imagine a few years ago. Current smartphones have so many sensors that we have just started to scratched the surface.
The interesting point is around technology. I am sure that engineers were not thinking about a distance measurement device when they place a mike and a speaker in your mobile phone. There will always be someone who will try to push the hardware and software to new limits. This already happened in the past with SMS, and the new hardware and software now available have just made that world closer to people willing to explore and innovate.
For sure you will not just place phone calls with your mobile. Not anymore.