Telephony, Telephones Dial telephone, 1929

Telephony, Telephones Dial telephone, 1929. AT&T introduced dial phones in 1919. Prior to this, the phone user contacted the operator who connected the call. However, this situation became impractical as more people started using telephone technology and the number of calls increased. The electronic switchboard was invented to cope with the increased demand. Using the new system, the user could dial the number they required and the switchboard would electronically connect the lines. The body of this telephone is made of moulded plastic. Phenol formaldehyde, more commonly known under its trade name Bakelite, is both a good electrical insulator and a robust material, and by the 1920s was established as a practical material from which to make telephones. Black was the most common colour, although ivory was also available. ©SSPL/Science Museum