It is a device capturing and controling all the signals, which are being created by the whole system, especially the made and received phone call signals. The device is mostly used for connecting regular phone system with the Internet and backwards.
A decade ago, call shops were the most convenient way for tourists and immigrants to contact their families. Today however, this has changed, the number of ways getting in touch with their families abroad has increased with the Internet, and currently it is threatening to the survival of the call shops.