Well this is actually a toy Land Rover which is adopted to be controlled with cellphone. Malik decided to use a cellphone as remote controller instead any other RF solution because of one major reason – the distance limitation. In fact using mobile phone you are only limited by GSM coverage which is almost everywhere.
But for this there are two mobile phones needed and both with active SIM cards. This way one mobile becomes a remote controller and another receiver. While in call sender can press any button on keypad and this way generate DTMF tone that can be decoded in receiving side. More complicated things are on Rover. First of all DTMF tone is decoded with MT8870 decoder and then signal goes to Atmega16 microcontroller which controls two motors via motor drivers L293D. So as a result you may end up with rover wandering far away from you blindly. Logical next step is to add some tracking solution.