As long distance lines between Tokyo and Osaka were completed on Feb. 1 of the thirty-second year of the Meiji Period (1899), the Solid Back magnetic telephone was adopted for long distance calls. This telephone had the same structure as the Delville type except for its Solid Back transmitter. The name "Solid Back" came from the fact that a vibration plate was placed behind carbon grains in the Solid Back transmitter. It enhanced sensitivity and reduced noise. When the service was started, the number of subscribers was about 178 in Tokyo and Osaka respectively and the conditions of calls were comparable to short distance calls. After that, service areas were extended to Kobe and Kyoto, and users increased.

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