In 1877, the St. Petersburg plant of the German company Siemens and Halske began releasing phones with two handsets, one for receiving and one for transmitting speech.
In the same year, an inventor called Vaden applied a telegraph key to call someone, which was later replaced by a button.
In 1877-78 a kind of telephone revolution began by the American scientist Thomas Edison. He invented the microphone with carbon powder (instead of a carbon rod). This invention was used virtually unchanged until the beginning of the 1990s and in some places still used today.
Significant contributions to the history of the telephone were made by Russian scientists. In 1878, the Russian electrical engineer P.M. Golubitsky applied a condenser in telephone headsets and developed the first 'original design' Russian telephone, in which several permanent magnets were used. And, in 1885, he invented a system of centralized supply of telephone microphones.
Credit for the development and improvement of the telephone belongs to an entire galaxy of scientists from different countries. The most well known are: F. van Rysselberghe, E. Berliner, F. Blake, A.E. Dolbera, T. Puskas, D. Hughes, C. Ader and others. A number of telephone devices were constructed by domestic inventors: R.R. Vreden, E.I. Gvozdev, A.A. Stolpovsky, F.I. Balyukevich, V.M. Nagorskiy, etc.
By the end of the 19th to the beginning of the 20th Century, when the 'birth' of the telephone was over, the global telephony boom took off and the construction of telephone exchanges was in full swing.