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One of the most important objectives in mobile communication systems is secure voice and data communication (including text, picture, video and voice) esp. in high bit rates. In this paper, a new procedure is proposed in which the intended data or voice is encrypted and modulated onto speech-like waveforms. The modulated waveforms are transmitted over the global system for mobile communications (GSM) voice channel and then demodulated and decrypted at the receiver. We propose an appropriate model for the GSM full rate (FR) speech codec by mapping data onto the fundamental parameters related to formants in a speech-like waveform including phases, frequencies and pitch frequencies. The proposed model has been evaluated for a GSM-to-GSM connection. Conducting different simulations we observed that the proposed approach results in a bit error rate (BER) of 0.02% when signal-to-noise ratio (SNR) is 15 dB in a 1.15 kbps channel. As a result, proposed method can be considered as a favorable choice for robustness to additive noise.