A data communication system comprises a radio frequency module, a baseband module, a memory unit, a parallel/serial module, a multimedia module, an image sensor module and a display module. The parallel/serial module performs digital signal processing and converts parallel bus data into serial bus data, and vice versa. The present invention provides an improved data communication method and system featuring a parallel/serial module that enables a serial data communication within cellular phone modules. The present invention will also reduce the cost of manufacturing and improve the performance of the cellular phone.