Mobile phones are turning into a growingly widespread educational tool across various contexts. However, the scope of research on teachers' role in mobile-oriented instruction is limited, much less examining how professional development influences their associated beliefs and practices. Grounded in sociocultural theory, this study aimed to fill some of the void by exploring the contributions of a professional development initiative framed around mobile phone usage to L2 teachers' beliefs and practices. Data were collected from semi-structured interviews, classroom observations, and online reflections. Data analyses indicated that the teachers gradually developed further awareness of educational exploitability of mobile phones and experienced restructuring in their associated beliefs. Additionally, the analysis of observational data showed direct and indirect patterns of utilizing mobiles by the teachers, undergoing changes during the research process. Results of the study offer implications for mobile-related teacher education, particularly professional development courses geared toward enhancing in teachers greater awareness of utilizing mobile devices.