How can an easy-access Mobile Phone Orchestra (MPO) platform be developed to facilitate high-end, flexible artistic expressions suitable for concert hall performances? Moreover, what challenges and possibilities arise in the development process of a novel MPO platform embracing school children as performers? In this paper, we discuss potential answers to these questions, which were integrated in the development process of mobilephoneorchestra.com. In particular, we highlight the main challenge of developing a performance platform that is both mobile and artistically rewarding, but still easily accessed by schoolchildren. Mobilephoneorchestra.com was developed as a Web Audio API to enable large-scale concert hall performances of fixed polyphonic contemporary art music. It is a kind of philharmonic orchestra for electronic sounds that embraces school children as performers and uses smart phones as instruments. Through an autoethnographic approach, our research was carried out in multiple iterations, inspired by action research. In this paper, we present findings from three iterations that include performances of music involving MPO. Schoolchildren/youths between 10 and 17 years old were addressed as MPO performers. The findings reveal both the artistic challenges of the platform and the possibilities. We specifically highlight the use of mobile music interfaces in combination with animated notation as a novel approach for an MPO concept.