Three model of the analogue telephone unit(“No.4 automatic desk telephone “, “600 form automatic desk telephone”,”601 form automatic desk telephone “) which NTT possesses is registered into “the history material of important scientific and technical ” of the National Science Museum in Japan.

“No.4 automatic desk telephone ” wass a telephone unit supporting the social activity of the postwar years of recovery. It was a technology original with Japan and was born in 1950.

“600 form automatic desk telephone” was a telephone unit corresponding to the mass demand of the high growth era.

“601 form automatic desk telephone ” was a telephone unit corresponding to the oil-crisis age after high growth. It achieved the large cost cut and the efficient maintenance.