CA2177759C
(en )
1999-10-05
Transmission of a data message during silent intervals of ringing for selection of terminal equipment
US4060700A
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1977-11-29
Two-party telephone system
US2592784A
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1952-04-15
Restricted service telephone system
US3193620A
(en )
1965-07-06
Supervisory control circuit for multiline telephone answering machine
US3133995A
(en )
1964-05-19
Call awaiting signal telephone circuits
GB212489A
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US2820848A
(en )
1958-01-21
Two-party line individual metering
US2020816A
(en )
1935-11-12
Automatic telephone system
US2274715A
(en )
1942-03-03
Calling apparatus
US2816170A
(en )
1957-12-10
Connector circuit party ringing selection
US1527820A
(en )
1925-02-24
Automatic telephone system
US3489857A
(en )
1970-01-13
Trunk connection arrangement for private telephone exchange
US1688656A
(en )
1928-10-23
Automatic telephone system
US1393806A
(en )
1921-10-18
Automatic telephone system
US1387353A
(en )
1921-08-09
Machine-switching telephone system
US2035594A
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1936-03-31
Telephone system
US2966555A
(en )
1960-12-27
Telephone selector and connector circuits
GB723997A
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1955-02-16
Automatic telecommunication exchange systems
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1921-10-18
Telephone-exchange system
US1204783A
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1916-11-14
Telephone-exchange system.
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1924-01-08
Telephone-exchange system
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1968-12-10
Calling-party identification system for party-line telephone exchanges
US1934384A
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1933-11-07
Telephone system
GB393583A
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1933-06-06
Improvements in or relating to telephone systems
GB680822A
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1952-10-15
Improvements in and relating to automatic telephone exchanges