I have developed the Rice Orbit Platform. The Rice Orbit platform consists of an Internet-capable mobile phone and its wireless body-area peripherals, including sensors and auxiliary user interfaces.
The latest version of the ultra low-power Orbit Sensor includes an MSP430 microcontroller, Bluetooth, LCD interface, MicroSD socket, 3-axis accelerometer, temperature sensor, an amplified analogue input, and a general-purpose interface with connections to ADCs, DACs, GPIOs, Serial/SPI/I2C, and other ports on the microcontroller. The microcontroller on the Orbit Sensor can individually power the various components on the board to minimize energy consumption.

Cellular and Wi-Fi networks have complementary strengths in energy cost and availability. Ideally, we should combine their strengths for energy efficient ubiquitous connectivity, but this is not an easy task. First Wi-Fi is not always available. Second, attempting a Wi-Fi connection is energy-hungry.
Our solution is to use context information to estimate network conditions in order to judiciously select the wireless interface for data transfer. We have published our work in MobiSys 07 [Link]. Our field-collected traces and our source code for Rate Logger and Tower Logger are now available. Our traces will also be available on the Crawdad Archive.