INTRODUCTION: Evidence shows benefit of digital technology for people living with human immunodeficiency virus on antiretroviral therapy adherence and retention in care, however, scalability and sustainability have scarcely been evaluated. We assessed participants' willingness to pay a fee for mHealth "Call for life Uganda" support, a mobile-phone based tool with the objective to assess sustainability and scalability. METHODS: "Call for Life study", approved by Makerere University, School of Public Health research & ethics committee, at 2 sites in Uganda, evaluated a MoTech based software "CONNECT FOR LIFE™" mHealth tool termed "Call for life Uganda". It provides short messages service or Interactive Voice Response functionalities, with a web-based interface, allows a computer to interact with humans through use of voice and tones input via keypad. Participants were randomized at 1:1 ratio to Standard of Care or standard of care plus Call for life Uganda. This sends pill reminders, visit reminders, voice messages and self-reported symptom support. At study visits 18 and 24 months, through mixed method approach we assessed mHealth sustainability and scalability. Participants were interviewed on desire to have or continue adherence support and willingness to pay a nominal fee for tool. We computed proportions willing to pay (± 95% confidence interval), stratified by study arm and predictors of willingness to continue and to pay using multivariate logistic regression model backed up by themes from qualitative interviews. RESULTS: 95% of participants were willing to continue using C4LU with 77.8% willing to pay for the service. Persons receiving care at the peri-urban clinic (OR 3.12, 95% CI 1.43-9.11.86) and those with exposure to the C4LU intervention (OR 4.2, 95% CI 1.55-11.84) were more likely to continue and pay for the service. Qualitative interviews revealed mixed feelings regarding amounts to pay, those willing to pay, argued that since they have been paying for personal phone calls/messages, they should not fail to pay for Call for life. CONCLUSIONS: Payment for the service offers opportunities to scale up and sustain mHealth interventions which may not be priorities for government funding. A co-pay model could be acceptable to PLHIV to access mHealth services in low resource settings. Clinical Trial Number NCT02953080.