This paper presents a novel user interface for handheld mobile devices by recognizing hand grip patterns. Particularly, we consider the scenario where the device is provided with an array of capacitive touch sensors underneath the exterior cover. In order to provide the users with intuitive and natural manipulation experience, we use pattern recognition techniques for identifying the users' hand grips from the touch sensors. Preliminary user studies suggest that filtering out unintended user hand grip is one of the most important issues to be resolved. We discuss the details of the prototype implementation, as well as engineering challenges for practical deployment.