I now understand, thanks. My engineering is a little rusty since I chose a totally different career.

Normally close for the Nak accessory power makes sense.
I hate to confess my ignorance but I have not installed a relay before - although I obviously do not think there can be much to it.

The activating, coil section, of the relay I assume should be fed by a hot wire and the mute ground. This way the loop closes when Nokia grounds the wire and the Normally closed circuit opens.