From Nokia's Conversation blog, we learn about their vision of turning mobile devices into sensors.
"Every phone is a sensor
When you start thinking of the mobile device as providing context, you start to think of users projecting who they are, what they are doing, and where they are. But, when you begin to think of what could mobile devices do anonymously, you can see cases where sensor-filled devices can, in aggregate, provide information on traffic, weather, or health patterns."
Most people see how the mobile phone could power context-aware applications by aggregating, analyzing and acting on information "sensed" by the device.