A component-based mobile device includes a server component for performing voice and data communication functions and a user interface (UI) unit for performing input/output functions. The server component is a larger unit with a larger server battery and more processing power and includes a engagement portion. The UI unit has a smaller UI battery and less processing power and is designed to fit within or removably attach to the engagement portion. The server battery may charge the UI battery when the UI unit is in the engagement portion. The server component and the UI unit may communicate wirelessly when the UI unit is out of the engagement portion and via a wired connection when the UI unit is in the engagement portion. The server component and the UI unit may be paired for encrypted wireless communication during the manufacturing process.