Background: To be consistent with the United Nations' sustainable development goals on gender equality, mobile health (mHealth) programmes should aim to use communications technology to promote the empowerment of women. We conducted a pre-trial analysis of data from the WelTel Retain study on retention in HIV care to assess gender-based differences in phone access, phone sharing and concerns about receiving text messages from a healthcare provider. Methods: Between April 2013-June 2015, HIV-positive adults were screened for trial participation at two clinics in urban slums in Nairobi, Kenya. Proportions of men and women excluded from the trial due to phone-related criteria were compared using a chi-square test. Gender-based differences in phone sharing patterns and concerns among trial participants were similarly compared. Results: Of 1068 individuals screened, there was no difference in the proportion of men (n = 39/378, 10.3%) and women (n = 71/690, 10.3%) excluded because of phone-related criteria (p-value = 0.989). Among those who shared their phone, women (n = 52/108, 48.1%) were more likely than men (n = 6/60, 10.0%) to share with other non-household and household members (p < 0.001). Few participants had concerns about receiving text messages from their healthcare provider; those with concerns were all women (n = 6/700). Discussion: In this study, men and women were equally able to participate in a trial of an mHealth intervention. Equitable access in these urban slums may indicate the ` gender digital divide' is narrowing in some settings; however, gender-specific phone sharing patterns and concerns regarding privacy must be fully considered in the development and scale-up of mHealth programmes.