A telecommunication terminal device includes a network connection unit having at least a first pin and a second pin to which a public telephone network is connected, and a third pin and a fourth pin through which a first external terminal device of a first type is connected to the first and the second pins; a first switching unit for selectively connecting the public telephone network with the first external terminal device and a second external terminal device of a second type; a first external terminal connection unit having a fifth pin and a sixth pin through which the second external terminal device is connected to the first and the second pins; and a feeding circuit connected to the first and the second pins to keep flow of currents provided from the public telephone network. The telecommunication terminal device is capable of exchanging telecommunication signals regardless of serial or parallel connection to additional external terminal devices.