A solid telephone, weighing over 20 kg, was manufactured after World War II as a mining telephone at the Signalling Equipment Manufacturing Plant (ZWUS). Originally, this type of telephone was used for communication in methane mines and rooms with a high risk of explosion. Its cast-iron construction, resistant to mechanical damage, allows it to be installed both outdoors (temperature range of -4°F to 140°F) and indoors, where there was significant dust and humidity (up to 95% relative humidity).

The telephone is waterproof, fireproof, and intrinsically safe, which also made it suitable for use in the railway and chemical industries.

Bárbara Bułdys (Museu da Universidade Jaguelônica, Collegium Maius)