US1924661A
(en )
1933-08-29
Telephone system
GB212640A
(de )
US2052051A
(en )
1936-08-25
Telephone system
US2021286A
(en )
1935-11-19
Telephone system
US1278330A
(en )
1918-09-10
Telephone-exchange system.
US2733295A
(en )
1956-01-31
lomax
US1393806A
(en )
1921-10-18
Automatic telephone system
US1688656A
(en )
1928-10-23
Automatic telephone system
US1647256A
(en )
1927-11-01
Selector-switch circuits for step-by-step systems
US1337753A
(en )
1920-04-20
Supervisory system
US2258660A
(en )
1941-10-14
Telephone system
US2154786A
(en )
1939-04-18
Telephone system
US1776653A
(en )
1930-09-23
Telephone system
US1772690A
(en )
1930-08-12
Telephone system
US3394230A
(en )
1968-07-23
Pcm signaling between central offices employing means to prevent unwanted ringing and to provide prompt disconnection of ringing signals
GB253986A
(en )
1926-06-21
Improvements in or relating to telephone systems
US1722538A
(en )
1929-07-30
Automatic telephone system
US1203502A
(en )
1916-10-31
Telephone-exchange system.
US1502877A
(en )
1924-07-29
Automatic telephone system
GB202618A
(de )
GB230214A
(en )
1925-03-12
Improved circuit arrangements for automatic telephone exchange systems
GB263210A
(de )
GB212985A
(de )
GB270068A
(en )
1927-05-05
Improvements relating to the metering of calls in automatic telephone systems
GB433956A
(en )
1935-08-23
Improvements in automatic telephone systems