The BTMC 2712 was introduced in 1927 and was for BTMC the very first fully integrated telephone in their product range.
The lower part of the housing was made of pressed steel and the upper part of zinc and aluminum alloy. This phone has many similarities with the Model 26 by Siemens & Halske.
There was also a wall version of this telephone, made of almost identical components. Only the upper part of the housing and the feet are different.
The telephone pictured here is from 1930 and has the original model handset (model 2288 a). This is the European version fo the so called E4 handset by Western Electric. The French PTT model 24 also has a version of this handset.
A phone in this configuration is a rarity nowadays. Most of them have a later model handset and the upper part has been stripped of paint and is copper plated, to give it a more antique look and feel.
Please find below the electrical diagram of this model: