With the end of World War I, new construction materials had been introduced into industries. Now telephone manufacturing companies were upgrading from workshops with manual production to mechanized factories. At the same time, a struggle began to merge many small workshops into one company in order to withstand the competition and the costs of purchasing and installing production machines. Thus, telephones from 1920 began to be made of metal. Iron, bronze and other metals gave way to wood. Telephones were now smaller and almost all parts were made of metal, the handle, the shell and the base. The telephone exchanges of that era acquired central arrays, thus eliminating the local batteries that wooden telephones had. Gradually, the ringing mechanism was integrated inside the device and the rotary dial appeared. The owner of such a telephone device calls the person he wants to talk to on his own, without the mediation of the operator… thus begins a small technological revolution in telephony that will grow in the following years.