The introduction of mobile communication technologies in health care in low- and middle-income countries offers an opportunity for increased efficiencies in provision of care, improved utilization of scarce resources, reductions in workload, and increased reach of services to a larger target population. Short message service (SMS) technologies offer promise, with several large-scale SMS-based implementations already under way. Still largely lacking in the research literature are evaluations of specific ethical issues that arise when SMS programs are implemented and studied in resource-limited settings. In this paper, we examine the ethical issues raised by the deployment of SMS messaging to support patient retention in HIV care and treatment and in the research conducted to evaluate that deployment. We use case studies that are based in Mozambique and ground our discussion in the ethical framework for international research proposed by Emanuel et al., highlighting ethical considerations needed to guide the design and implementation of future SMS-based interventions. Such guidance is increasingly needed in countries such as Mozambique, where the local capacity for ethical study design and oversight is still limited and the scale-up and study of mHealth initiatives are still driven predominantly by international collaborators. These issues can be complex and will need ongoing attention on a case-by-case basis to ensure that appropriate protections are in place, while simultaneously maximizing the potential benefit of new mHealth technologies.