A switching device for providing selective telephone access to multi-telephone line and data line sources. The device can be incorporated within a compatible device or configured as a stand-alone, self-contained device. In the later configuration, it includes a housing, an input port for receiving multiple telephone or data lines and an output port for connecting a compatible device, such as a computer modem, to one of the telephone lines. Switching means are provided for selectively connected the compatible device to one of the multi-telephone or data line sources and for selectively blocking access to the multi-telephone or data line sources. Indicator means are further provided for identifying which of the multi-telephone or data line sources are being connected to the compatible device and whether access is being blocked to the multi-telephone or data line sources.