NEC Electra Elite 48/192 Features And Specifications Manual page 392

Electa Elite
Features and Specifications Manual
When the ICM key is pressed during a normal incoming CO/PBX call,
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intercom dial tone is provided to allow an internal call.
System Software S5000 or higher is required.
Using System Software S4500 or lower, the incoming call is
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answered if the ICM key is pressed.
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