| 摘要 |
A telephone switching system is provided for use with an external telephone line and a plurality of telephone extensions wherein each extension has a plurality of "touch tone" buttons which, when depressed, generate an audio signal unique to that button. The system includes at least one internal channel and at least one external channel wherein the external telephone line is connected to the external channel. An on-hook and off-hook detector is provided for each of the telephone extensions as well as a detector for detecting the presence of an incoming call on the external channel. A switching circuit is then responsive to an off-hook status of a first extension together with a coded audio signal generated by the buttons at the first extension to either (1) selectively and exclusively connect the first extension to a selected second extension determined by the coded audio signal to the internal channel and to generate a ring signal to the second extension, or (2) connect the first extension to the external channel. The switching circuit is also responsive to a coded audio signal to transfer an incoming call from the first extension to a selected second extension. Other features, including area code lockout features and placing an external call on hold, are also disclosed.
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