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A description of equipment providing acoustical transmission over ordinary telephone lines and utilizing standard telephone handsets is presented. Included is a discussion of the more pertinent parameters which determine the final design of the equipment. Among them are proper orientation of the granular carbon transmitter, maximum line bit rates, and tolerable total harmonic distortion. The frequency and transient response of all acoustical transducers employed in the equipment are presented. The results of local and cross-country tests are summarized; also included is a summary of the actual operational experience over a period of two years from large numbers of units in use over the entire country.