The image shows the telephone exchange of the main post office in Frankfurt am Main before 1900. It was primarily women who worked as telephonists from the 1880s onward, receiving calls and transferring them.
Main post office of Frankfurt am Main, telephone exchange with a switchboard, 19th century, black-and-white photograph, ca. 1900, photographer: Horst Ziegenfusz; source: Collection of the Historisches Museum Frankfurt, in: Dorothee Linnemann (ed.): Damenwahl! 100 Jahre Frauenwahlrecht: Begleitbuch zur Ausstellung, Frankfurt am Main 2018, p. 26; via: Wikimedia Commons, https://commons.wikimedia.org/wiki/File:Telefonzentrale_mit_Klappenschalter_Frankfurt_vor_1900.jpg, Creative Commons Attribution-Share Alike 4.0 International (CC BY-SA 4.0), https://creativecommons.org/licenses/by-sa/4.0/deed.en.