A mobile communication terminal device equipped with a replaceable communication module and a back cover thereof are provided. The mobile communication terminal device includes: a host processor configured to control and operate the mobile communication terminal device; a baseband processing unit configured to process a mobile communication protocol; and a radio frequency (RF) signal processing unit configured to wirelessly communicate with a mobile communication network, wherein the host processor, the baseband processing unit and the RF signal processing unit are further configured to be implemented as modules that are attachable to or detachable from a printed circuit board (PCB) of the mobile communication terminal device.