Implementation of a modem which transmits digital data on GSM voice channel In this work, the GSM modem was designed in order to use GSM voice channel in digital data transmission. First, the method which was used for designing of modem was explained. Then, the system was implemented on Spartan 6 and MicroBlaze as hardware software co-design. Some software-hardware enhancements and some performance improvements were carried out through results of tests. In the final step, we offered suggestions regarding to future works.