The system has an exchange line, a switching console, several extensions able to dial an exchange and a device to transfer and evaluate codes. A timing circuit is set when the receiver of an extension is lifted with the code of the outgoing engagement in a computer shared by all extensions. After the timing circuit time has elapsed, a connection to the exchange is established if no selection has occured within this time. Lines within the house that are already engaged cause an acoustic signal to be generated when they are selected. The acoustic signal appears at the same time as the timing circuit is set.
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