Regardless of Head unit - assuming it's a standard VX / GM Unit, the simplest way is to use an Autoleads 06-109B telemute lead.
This connects to the telephone pre-wiring which is located above the glovebox (if not previously used) or it will be hanging down underneath the right hand side of the glovebox if it's been used before.
This will connect to a Nokia CK-7W Bluetooth kit that you can buy cheaply from Ebay or with some slight modification you can use other car kits.
The Nokia Microphone lead can run up the passenger A pillar and under the roof lining and through the centre overhead lamp assembly where the microphone can be stuck
You know I might just have a go at this myself. I have a HFW-1 along with the controller etc sitting in the garage doing nothing and it's got to be better than the Supervoice thing I am using now. Do you know what the differences are between the HFW-1 and the HX-5?
I don't suppose you know the wiring colours that I would need to connect to on the telephone pre wiring multiplug for me to wire the HFW-1 into by chance do you or will I have to search it out via TIS?
I take it there would be no problem with it muting a feeding the audio through a NCDC2013 as I know they were designed to work with the phone kit anyway.