Abstract: Mobile telecommunication service system and method using a public frequency are provided. The method includes receiving a call connection request for a certain recipient from a mobile communication terminal; and connecting a radio interval between the mobile communication terminal and a Base station Transceiver Subsystem (BTS) of a call connection interval of the mobile communication terminal and the certain recipient, using a public frequency band. Accordingly, it is possible to stably connect the call to the public institution in case of the emergency or the public operation. By raising the utilization of the limited frequency resources, the insufficient frequency in the private mobile telecommunication can be addressed. The public institutions provide the public frequency to the private telecommunication companies and use the mobile communication service for free or at a low cost in return.