There is a substantial body of research on mHealth interventions in low-resource settings, but little empirical understanding of use by staff in established health facilities. What evidence there is indicates divergent outcomes. In order to generate insight into this phenomenon we undertake an exploratory study of mHealth use in several public clinics, where the staff are required to perform a simple registration process for the MomConnect system. We draw on the lenses of Activity Theory and affordance actualisation to assist in the analysis of the evidence collected, and find that professional identities, local priorities and technology features all interact in shaping the forms that mHealth use takes in practice. Based on this analysis we propose a set of higher-level concepts in order to compare case studies of mHealth use. This research contributes to theory by proposing a framework for understanding mHealth use in existing facilities, with specific reference to low-resources settings. In addition we contribute to the literature on conceptualising affordance actualisation, drawing on Activity Theory. Finally, we inform practitioners by outlining important constraints that impede staff as they strive to accommodate this additional burden in their daily routines.