Old telephones used to have mechanical keys and no displays, and they started to be used from the 19th century. In these telephones, electricity was transmitted through telephone lines to the desired location. Old telephones were very heavy and large and were only used in public places like train stations, hotels, libraries, and post offices. With the passage of time and the development of technology, telephones became smaller and, especially with the availability of higher-quality lines via fiber optics and methods of encoding calls, mobile and smartphones were invented and are now among the most powerful and useful communication devices.