Adherence to antiretroviral therapy (ART) is a major challenge for people living with HIV (PLWH). The purpose of this pilot study was to evaluate the six criteria for a phone-based intervention program for PLWH in Indonesia using a mixed methods feasibility study design. PLWH were included who took ART for at least 3 months, who had a cell phone, access to the internet, and the WhatsApp application. Thirty eligible respondents completed demographic information and shared their daily ART frequency during the enrolment visit. Motivational and health promotion messages were sent in the form of text message, images, and video links 30 min before their scheduled medication time for 3 months (October-December 2020). All respondents were retained until the end of the program. Necessity: Identified a need to be reminded when their ARTs were due. Feasibility: The participants were used to WhatsApp in their daily lives. Acceptability: The respondents responded well to the messages. Safety: None of the respondents experienced a mental distress due to involuntary HIV disclosure or stigma. Fidelity: The program delivered 79 to 91% of the messages. Challenges of the phone-based program centred around technical issues, human error user error, and environmental problems. Cost: The program could be delivered for less than $3 a day. The program met the six criteria for a useful intervention and can be applied to promote adherence to ART in remote regions of Indonesia. © The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2025.