A system and method for data communication over a cellular communications network that allows the transmission of digital data over a voice channel using a vocoder that monitors parameters of a Levinson Durbin recursion and then uses full rate CELP if the monitored prediction error falls to below a predetermined threshold within a pre-selected number of iterations of the recursion. The system and method encode digital data to be transmitted using a continuous signal modulation technique at a selected bit rate and one or more frequencies that are selected such that the resulting modulated carrier signal is processed by the vocoder using full rate CELP as a result of the monitored prediction error.