SETTING: India and South Africa shoulder the greatest burden of tuberculosis (TB) and human immunodeficiency virus (HIV) infection respectively, but care retention is suboptimal.OBJECTIVE: We conducted a study in Pune, India, and Matlosana, South Africa, 1) to identify the factors associated with mobile phone access and comfort of use, 2) to assess access patterns.DESIGN: A cross-sectional study assessed mobile phone access, and comfort; a longitudinal study assessed access patterns.RESULTS: We enrolled 261 participants: 136 in India and 125 in South Africa. Between 1 week and 6 months, participant contact decreased from 90% (n = 122) to 57% (n = 75) in India and from 93% (n = 116) to 70% (n = 88) in South Africa. In the latter, a reason for a clinic visit for HIV management was associated with 63% lower odds of contact than other priorities (e.g., diabetes mellitus, maternal health, TB). In India, 57% (n = 78) reported discomfort with texting; discomfort was higher in the unemployed (adjusted OR [aOR] 4.97, 95%CI 1.12-22.09) and those aged ≥35 years (aOR 1.10, 95%CI 1.04-1.16) participants, but lower in those with higher education (aOR 0.04, 95% CI 0.01-1.14). In South Africa, 91% (n = 114) reported comfort with texting.CONCLUSION: Mobile phone contact was poor at 6 months. While mHealth could transform TB-HIV care, alternative approaches may be needed for certain subpopulations.