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Building a telephone network was a great challenge for the post-war Czechoslovak economy and was finished only in the end of the 20th century, when it already started to be replaced with mobile phones. There are three types of wired telephone lines - a "local battery", "central battery" or "automatic" line. The commonly used phones with number dial are of the Automatic type, they were connected to an automatic telephone exchange that would provide the connection depending on the dialed number. This system was created at the beginning of the 20th century and the basic design of the phones did not change until the 1980s, only the look and materials differed. Thanks to the development of electronics, the rotary dials were later replaced with button dials with memory systems and so on.
The Local Battery and Central Battery systems provide connection only between two phones, there is no way to select more users, the telephones do not have any number dial. If they were to be connected into a telephone network, a manual exchange would be used. The user would pick up the phone, the Central Battery system would automatically show the connection request to the exchange operator. Local Battery user would have to turn a crank connected to a small alternator and the produced current would power an indicator on the exchange. Then the operator would ask the user about the desired connection and would manually connect them to the other user with a switchboard. Manual telephone exchanges were used in some citites well until the 1980s. The Local Battery system is still used whenever a simple connection between two places is needed, e. g. on railway or in mines. The telephones are connected with a two-wire line and after the crank is turned, the other phone starts to ring.
Phones were manufactured in Tesla Prague-Karlín at first, later the production moved to Stropkov and Liptovský Hrádok in Slovakia. These factories still exist and produce telecommunication components.
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