US3697702A
(en )
1972-10-10
Selectably controllable announcement system
GB798749A
(en )
1958-07-23
Improvements in or relating to automatic telephone exchanges providing automatic transfer service
US2691066A
(en )
1954-10-05
Automatic telephone system
NO126052B
(enrdf_load_stackoverflow )
1972-12-11
US2727947A
(en )
1955-12-20
Combined telephone and paging system
GB1268151A
(en )
1972-03-22
Improvements to selection systems for electrical circuits
GB698848A
(en )
1953-10-21
Improvements in or relating to private automatic branch telephone exchanges
US2447494A
(en )
1948-08-24
Telephone register control system
US2520130A
(en )
1950-08-29
Night switching for private automatic branch exchanges
US2172579A
(en )
1939-09-12
Key sender
US2976368A
(en )
1961-03-21
Incoming trunk circuit for in-dialing service
US3251949A
(en )
1966-05-17
Intergroup transfer circuit
US2185287A
(en )
1940-01-02
Telephone system
US3502818A
(en )
1970-03-24
Call forwarding system with timed cancellation
GB704441A
(en )
1954-02-24
Automatic telephone systems provided with toll recording facilities
US2574943A
(en )
1951-11-13
All relay private automatic telephone system having connections to one and two digit trunks
US1640085A
(en )
1927-08-23
Service-observing apparatus for automatic telephone systems
US1795350A
(en )
1931-03-10
Service observation in telephone systems using call indicators
GB617932A
(en )
1949-02-14
Improvements in telephone switching systems
NO116699B
(enrdf_load_stackoverflow )
1969-05-05
US2542749A
(en )
1951-02-20
Telephone intercept system
DE750213C
(de )
1944-12-20
Schaltungsanordnung fuer Fensprechnebenstellenanlagen mit Waehlerbetrieb
US2651680A
(en )
1953-09-08
Dual-use register sender
US3387094A
(en )
1968-06-04
Call number indicating circuits
US2288789A
(en )
1942-07-07
Telephone system