Tapan Parikh describes his experiences developing CAM - a toolkit for mobile phone data collection - in the rural developing world. Designing technologies for an unfamiliar context requires understanding the needs and capabilities of potential users. Drawing from the results of an extended participatory design study conducted with microfinance group members in rural India (many of whom are semi-literate or illiterate), he outlines a set of user interface design guidelines for accessibility to such users. The results of this study are used to motivate the design of the CAM toolkit, which includes support for paper-based interaction; multimedia input and output; and disconnected operation. Parikh discusses possible topics for future work and his long-term research vision. From the Series:CSE Colloquia - 2007