This talk explores the smartphone design space to achieve energy sobriety. At its core, the proposed platform has a compute-limited but energy efficient microcontroller (MCU). Another processor can be attached to execute legacy Linux applications. Some tasks are offloaded to the Wi-Fi network controller. Our design prefers an energy-efficient variant of the 4G cellular network, which is turned off as often as possible. We are in the process of designing a hardware evaluation board to implement the vision presented in this talk.