In for one. Though the concept is little counter intuitive (use of phone sensors as extended sensors for Arduino), it is the software that is attractive

1Sheeld is a new easily configured shield for Arduino. It is connected to a mobile app that allow the usage of all of Android smart phones\’ capabilities such as LCD Screen, Gyroscope, Switches, LEDs, Accelerometer, Magnetometer, GSM, Wi-Fi, GPS …etc. into your Arduino sketch.

via 1Sheeld: Replace your Arduino shields with your smart phone! by Integreight, Inc. — Kickstarter.