In this paper we present a case study of a longitudinal in-situ observation that involves a new social application for mobile communication. Our study demonstrates the need for an adaptive approach to planning, design, and implementation that is responsive to emerging social and infrastructure conditions. This represents a shift from traditional longitudinal studies that observe prototype systems with fixed sets of affordances. In the case of mobile and social applications there is a complex interaction between the social dynamics, the new technology, and the mobile infrastructure. Exploratory research thus requires approaches that can deal with such complex conditions. That includes a high level of prototype plasticity to ensure adoption and sustained use that is needed for longitudinal in-situ research. The social aspects dictate specific forms of instrumentation to enable observation of social interactions and mechanisms to inject the new technology into an existing social and communication ecosystem. Our study demonstrates the evolving use of complementary techniques and in-situ modifications of the prototype to support longitudinal observations in a real setting.