NEC 900i Installation And User Manual page 17

In program 0909 - Extension Ring Group Assignment:
1. Assign the cordless phone's extension to a Ring Group.
In addition to the other normal keyset programming, the following programs
can be set so an optional desk phone can be used in addition to the cordless
phone:
In program 1009 - Cordless/Desktop Extension Assignment:
1. Assign the extension number for the cordless phone first and then
assign the extension for the desk phone.
In program 1006 - Programming Function Keys:
1. Program a function key to be a Call Coverage key for the cordless
phone's extension as well as the desk phone's extension. Assign
the desk phone's extension to the cordless phone and the cordless
phone's extension to the desk phone (enter code 1036 + extension
number).
In program 1016 - Multiple Directory Number Ring Assignment:
1. Set the ringing assignment for the Call Coverage key for both the
cordless phone and desk phone's extension (Option 1 allows the
calls to ring the extension).
System Programming
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