In this paper we present development of a mobile-based Unstructured Supplementary Service Data (USSD) system that will be used to screen people who have had contact with an infectious TB patient. The USSD-based system prototype is implemented using a simulator as a prelude to actual development. USSD technology allows interactivity between the system and the contact through session-based messaging. Since access to the USSD system is only through service providers, we chose to use an open-source simulator, the mchoice simulator, to develop a prototype in order to identify potential issues that may arise when using the system; determine usability and acceptability of the system by users, and to elicit further requirements for future development efforts. The paper presents the results of usability goal tests of effectiveness, efficiency and satisfaction on the simulated system, together with interesting observations by users that will serve as important pointers in finalizing the requirements of the final system.