Key telephone system with a common push-button sender system

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H04M 172

Patent

active

040229858

ABSTRACT:
A large scale key-telephone system or telephone exchange system having approximately eighty extension channels and a push-button dial system has been disclosed. A common unit in the system is a DTMF oscillator, which is installed in each telephone set, according to a prior art. The present system is completely compatible with thus prior key-telephone system or exchange system.

REFERENCES:
patent: 3301967 (1967-01-01), Plyer
patent: 3420961 (1969-01-01), Averill, Jr.
patent: 3603737 (1971-09-01), Le Dorh et al.
patent: 3701854 (1972-10-01), Anderson et al.

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