This evaluation of a newly designed smartphone application (app) for linkage to care, HIV treatment adherence and retention in care, is taking place at five Johannesburg health facilities. Intervention allocation is random with individuals either receiving the smartphone app or standard of care. The trial is motivated by evidence from elsewhere that sending lab results via app acceptable, and loss of patients in need of HIV care can be reduced with mobile Health interventions. There is a growing number of smartphones in South Africa (at the time of baseline assessment, about 40% of the surveyed population had an Android smartphone with data, and the majority of new phones are smartphones). The trial's objectives are: a) Test whether routine linkage to HIV care at public sector services is improved by providing HIV positive clients with a smartphone-enabled app when compared to standard of care; b) Determine HIV treatment initiation rates between intervention and control arm; c) Test the feasibility and acceptability of receiving lab results via app; d) Assess secondary effects from improved participant information, including return rates after falling out of care, participant satisfaction, and rates of repeat blood tests; e) Determine knowledge levels on HIV care; and f) Assess the effect in priority groups for better linkage to care (male HIV cases and HIV positive youth). If data allow, a cost-benefit analysis will also be conducted.