Mobile phones are increasingly being used to enhance the effectiveness of health programs by engaging individuals in discreet and ongoing ways. Mobile phone health interventions, called mHealth, can also improve the availability and quality of operational research data. mHealth interventions have successfully been used in developing countries to collect health data, increase access to health knowledge and increase medication/appointment adherence. But, few mHealth interventions have been rigorously evaluated. There is strong evidence that mobile phone messages can be successfully used to support preventative healthcare, such as maternal postpartum visit attendance in Kenya. There is also evidence that self-report of risk behaviors through a mobile phone is a method of data collection that is as reliable and valid as in-person surveys. Especially for mobile or hidden populations in developing countries, mobile phones may become our most important tool for linking people to health services.