Interactivity in the classroom is reported to promote a more active learning environment, facilitate the building of learning communities, provide greater feedback for lecturers, and help student motivation. Various definitions of interactivity exist in the literature, alternately focusing on the participants, structure and technology. The "PLS TXT UR Thoughts" research project builds on existing definitions to define interactivity as a message loop originating from and concluding with the student. The authors chose to introduce mobile phones and short message service (SMS) within the classroom due to the ubiquity of mobile phones among students and the interactive potential of SMS. SMS is a low-threshold application used widely by students to quickly send concise, text-based messages at any time. The research presented involved students sending SMS in real-time, in class, via their personal mobile phones. Using a modem interfacing with customised software to produce SMS files, the lecturer can view the messages and verbally develop the interactive loop with students during class. The SMS are available online after class, allowing interactive loops to further develop via threaded comments.