The various embodiments described herein generally provide apparatus, systems and methods which facilitate the transmission of data between a client device and a remote device over a voice channel of a telephone network. More particularly, data from a client device is modulated into an audio signal using multiple frequency shift keying (MFSK) techniques and transmitted to the remote device over a voice channel of a wireless telephone network during a phone call. The frequency of the audio signal is selected based on the value of the data to be transmitted. The remote device receives the audio signal and determines the frequency of the audio signal to extract the transmitted data.