Grassroot Soccer (GRS) is exploring the effectiveness of a two-way SMS campaign delivered through a single-sex, soccer-based HIV prevention programme. The campaign aims to enhance reproductive health and rights outcomes among at-risk adolescent South African girls ages 11-14. To test and refine the SMS campaign prior to piloting, GRS employed a participatory process in building a prototype of an Unstructured Supplementary Service Data (USSD) line using Open Data Kit (ODK), an open-source application for building, collecting, and managing data on Android-enabled phones and tablets. The USSD prototype was delivered to 72 female participants and coaches in July 2013. All participants also completed a 10-item questionnaire on ODK. Focus group discussions were conducted with coaches (N=1 group) and parents (N=1 group). Results demonstrate that 55% of participants reported owning a mobile phone; a majority reported being "very interested" in the USSD prototype (68%) and "very comfortable" interacting with the USSD prototype (62%). Findings suggest that two-way SMSs could offer an acceptable service for reaching at-risk adolescent girls in South Africa with health-related messaging, particularly on sensitive issues. Results will inform delivery of a USSD line in a programmatic pilot and assessment to be carried out in six primary schools (approximately 600 participants) in Soweto, separated between control and intervention groups, beginning in September 2013.