A main terminal and a method of operating the same. In this method of operating the main terminal, the main terminal is connected to a telephone network so as to communicate with the telephone network, and selectively connects an external terminal to the telephone network. To perform the method, first, if it is requested that the telephone network be disconnected from the external terminal and instead be connected to the main terminal, an internal current to flow into the main terminal is obtained from a loop voltage generated when the external terminal is in connection with the telephone network. Next, the internal current is applied to the main terminal. Thereafter, the telephone network is disconnected from the external terminal and instead connected to the main terminal. While the internal current is flowing in the main terminal, the main terminal maintains the loop voltage generated when the external terminal is in connection with the telephone network. Accordingly, the telephone network can be disconnected from an external terminal and instead be connected to the main terminal without generating an interrupt. Thus, an exchanger included in the telephone network can be prevented from malfunctioning due to the generation of the interrupt.