Panasonic KX-TCD540NZM Service Manual page 32

NOTE:
When you put a first digit on step 9, it must overwrite the current displayed
numbers. We recommend you to write down the restricted phone number you
entered.
6.11. Call BAR On/Off (Call Prohibition On/Off)
When this feature is set to ON, outgoing calls cannot be made. Intercom calls and
calls to numbers assigned as emergency numbers can be made.
6.11.1. Base Unit
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