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1919
1921
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1920

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C.1920 Gray Telephone Pay Station Co Hartford CT
C.1920 Gray Telephone Pay Station Co Hartford CT
Gray Telephone Pay Station
Demonstration telephone
Demonstration telephone
E. F. Caldwell & Co. Custom Handmade Candlestick
E. F. Caldwell & Co. Custom Handmade Candlestick
Gray Three-Slot Payhone
Gray Three-Slot Payhone
Gray Telephone Pay Station
Keystone Dial Candlestick
Keystone Dial Candlestick
American Electric Keystone Telephone
Siemens & Halske Naval Telephone
Siemens & Halske Naval Telephone
Siemens and Halske 25-extension intercom
Siemens and Halske 25-extension intercom
Siemens
Tønsberg Telefonforening telephone
Tønsberg Telefonforening telephone
Otto Zobel invents m-derived filters
Otto Julius Zobel
PDF: AT&T Annual Report, 1920
AT&T Annual Report, 1920
Dial phones spread to major cities
Sosthenes Behn founds ITT
Sosthenes Behn