This paper examines the origins and motivation for the Pocket Gamelan, a performance interface for mobile phones where musical interaction between players is facilitated via bluetooth. The performance scenario for mobile phones has its origins in two works composed more than 25 years earlier. Mandala 1, composed in 1980 and Mandala 2, in 1981, were the first in a series of works in which an ensemble of players swing mobile sound sources while Mandala 3 and Mandala 4 were composed to be performed using bluetooth-enabled mobile phones. The Mandala series all have a common feature related to microtonal tuning. While the later works Mandala 3 and Mandala 4 have specific just intonation tuning characteristics that represent a particular system, the earlier works Mandala 1 and Mandala 2 are based on two different arbitrary approaches to tuning. Mandala 1 is based on the interaction between pitches in found objects and microtonally tuned sound sources while Mandala 2 is based on just intervals selected gratuitously by each player. The original sound source consisted of a twin-T oscillator, battery-powered amplifier and loudspeaker. These were mounted in plastic kitchenware which is attached to a cord and physically swung to produce audio chorusing. Like the Pocket Gamelan, the original instruments were designed for performance by large ensembles of non-expert players. The paper summarises common features of works created for both Tupperware Gamelan and Pocket Gamelan through a window onto what is perhaps an unprecedented period of change that has taken place in musical instrument technology over a quarter f a century.