Name M´┐Żnzfernsprecher 28 (Coin Telephone 28)
Maker DBP (Deutsche BundesPost / German Federal Post Office)
Date 1928

Already relatively early there were public public telephone boxes, which were still rather simply developed however at the beginning: One removed the receiver and turned at the crank. Thereupon "Ms of the office" announced itself and requested to throw a coin into the apparatus. The coin fell now in the free case into the housing and met at the end of its flight a metal bell. In the switching center one knew now that the participant had paid.

So similarly also the apparatus illustrated above functioned. The different coins fell on different bells, which produced appropriate tones. (only with long-distance calls.) Thus it looked from the inside:
12 cartridge slot safety device, 14 intake channel with segregating, 15 drop channel, 16 sound mechanism, 17 trap channel, 20 segregating judges, 21 coin shute

23 return levers, 28 coin contact, 30 check magnet, 32 taking the money, 31 Muenzfuehlhebel

Today coin phones are threatened from becoming extinct, map and mobile telephones make for them life hard.
Some pictures of the 1938 model-