This paper describes the prototype for a set of mobile instruments in which java phone technology has been adapted for performing microtonal music. The prototype was developed using widely available mobile phone handsets instead of building new hardware. The paper discusses aspects of j2me development together with limitations of the mobile platform used for the project. Development issues such as real-time audio, microtonal MIDI implementation and control using Bluetooth communication are discussed. The paper also describes tools developed so existing algorithmic composition and tuning software can be used to compose music for mobile devices. It concludes with discussion of various performance scenarios for mobile electronic instruments to realise music composed in tuning systems outside twelve-note divisions of the octave.