US3904834A
(en )
1975-09-09
Handsfree loudspeaking key telephone set and a switching circuit for use in a microphone and loudspeaker equipped key telephone
US3254159A
(en )
1966-05-31
Telephone adapter
GB1055633A
(enExample )
US2200820A
(en )
1940-05-14
Automatic telephone system
US2249156A
(en )
1941-07-15
Telephone system
JPH0451111B2
(enExample )
1992-08-18
US1325347A
(en )
1919-12-16
Telephone system
US2897285A
(en )
1959-07-28
Intercommunicating system
GB635644A
(en )
1950-04-12
Improvements relating to telephone systems
SU1570025A1
(ru )
1990-06-07
Устройство громкоговор щей конференцсв зи
JPS6328554B2
(enExample )
1988-06-08
GB677894A
(en )
1952-08-27
Improvements in or relating to intercommunication telephone systems
US2644039A
(en )
1953-06-30
Circuit arrangement for conference call installations
US2238070A
(en )
1941-04-15
Broadcast switching system
US2848552A
(en )
1958-08-19
Loud-speaking station for automatic telephone systems
US1325871A
(en )
1919-12-23
Chables w
GB597893A
(en )
1948-02-05
Loud speaking telephone systems
GB701947A
(enExample )
US809929A
(en )
1906-01-16
Intercommunication telephone system.
US2254723A
(en )
1941-09-02
Subscriber line circuit
KR920002956B1
(ko )
1992-04-10
사설교환기에 있어서 교환대의 유선방송 및 응답방법 및 회로
JPH0122797B2
(enExample )
1989-04-27
JP2815878B2
(ja )
1998-10-27
家庭用簡易電話交換装置
JPS5910832Y2
(ja )
1984-04-04
コ−ドレス電話装置
US1870471A
(en )
1932-08-09
Telephone system