Here's a very nice early 20th century telephone specifically designed for internal systems in large houses etc. Requires 3 wires to connect to another telephone using a 6volt DC supply for speech and to operate the bell. There is a push-button on top to call the other telephone and a grip-switch in the handset which is operated to enable conversation to take place. Was in use for a couple of years but has now been superseded by a more modern 1930s design. Diagram included but no makers name is evident, probably made in Coventry by Peel-Connor who made similar designs for GEC. From a pet and smoke free home.