This paper discusses a new approach to computer music synthesis where music is composed specifically for performance using mobile handheld devices. Open source cross-platform computer music synthesis software initially developed for composing on desktop computers has been used to program a Linux phone. Work presented here allows mobile devices to draw on these resources and makes comparisons between the strengths of each program in a mobile phone environment. Motivation is driven by aspirations of the first author who seeks to further develop creative mobile music performance applications first developed in the 1980s using purpose-built hardware and later, using j2me phones. The paper will focus on two different musical implementations of his microtonal composition entitled Butterfly Dekany which was initially implemented in Csound and later programmed using Pure Data. Each implementation represents one of the two programming paradigms that have dominated computer music composition for desktop computers namely, music synthesis using scripting and GUI-based music synthesis. Implementation of the same work using two different open source languages offers a way to understand different approaches to composition as well providing a point of reference for evaluating the performance of mobile hardware.