New innovations in mobile technology provide an unparalleled opportunity for researchers and organizations to scale communications with citizens in the developing world, but bring new challenges in terms of how to generate and retain engaged users. We report on a number of technical dimensions based on our experience building a bi-directional multi-channel mobile phone platform to engage citizens in South Africa's 2014 presidential election. Specifically, we deployed the “VIP:Voice” platform at national scale to conduct opinion polling, to allow citizens to report on political activity, and to engage citizen monitors for polling stations on election day. Our platform operated across multiple device types, from flip-phones to Twitter, and co...