In South Africa, HIV-positive women receiving antiretroviral therapy often are lost to care postpartum; strategies to support long-term engagement are needed. Mobile health (mHealth) interventions are emerging as a possible solution for supporting long-term engagement in the prevention of mother-to-child transmission (PMTCT) of HIV care continuum. In order to explore acceptability and feasibility of mobile health (mHealth) interventions in this context, we conducted focus group discussions (FGDs) to assess trends in smartphone usage in postpartum women. In six FGDs, we interviewed 27 HIV-positive, postpartum women who attended regular care at the Gugulethu Community Health Centre in Cape Town, South Africa, and who use a smartphone. Questions assessed the respondent's general trends in smartphone use, as well as their exposure to and perceptions of mHealth interventions. We found little turnover in phones and phone numbers, and about half the participants shared their devices with family and friends. Respondents reported high familiarity with smartphone applications, including WhatsApp, Facebook, YouTube, and Twitter, with WhatsApp as their preferred method of smartphone communication. Data bundles were most often used to connect to the internet, motivated by the perception that data bundles last longer and are cheaper than airtime, but respondents were adept at locating Wi-Fi sources at work or other public spaces. Nearly all participants were familiar with MomConnect, a national mHealth text support service in South Africa, and most described it positively. Respondents expressed interest in future HIV mHealth applications including complementary health information on physical activity, nutrition, mental health and basic social services. Participants were active and engaged smartphone users with reliable internet connections and a positive attitude towards mHealth platforms. Future mHealth interventions show promise in this population.