Mitchell, Bridger M., Utilization of the U.S telephone network / Bridger M. Mitchell, Tenzing Donyo. - xv, 52 pages : illustrations ; 28 cm. - Rand ; MR-436-EAC/WIK . - Rand ; MR-436-EAC/WIK . Subjects--Topical Terms: Telephone--United States. Communication and traffic.