As the features of mobile phones are being enhanced and the performance is being greatly improved, the generic operating systems are being incrementally used in mobile phones. However, since the mobile phones have different requirements in both features and performance compared with desktop or server systems, the operating systems for generic systems could not be used without customization and modification. This case study paper describes the design and implementation of a Linux-based smartphone hardware and software. The enhancements and additional implementations in both kernel and middleware layers are explained. As an experiment, the power consumption of the implemented mobile phone under a number of user scenarios has been measured.