This handsome set of telephones was constructed 75 years ago according to plans contained in the May 1951 issue of the British Practical Mechanics.

As with many electronic projects of the era, it was constructed from available surplus components, namely handsets with a low-impedance ear piece, carbon microphone, and push-to-talk button.  The button was pressed into service as a call button for the other station.  This example was constructed for use in a cinema, hence the signal light.  But the author pointed out that a bell could just as easily be used.

For larger setups, a switchboard could be constructed to connect the various stations.