Hawks, There is a good chance it will work. I was at a site that had 9640s with the IP Phone Bluetooth Adapter.
Setup was painless. I believe they had Plantronics Bluetooth sets.
On the phones "Avaya" menu button hit "options & settings", then "advanced settings", and then "Bluetooth"
Once your in the Bluetooth Menu, It will show device its paired with, if any. You will have the option to "change" / "disable" If there no device You will have the option to "add"
One You have the headset paired, you will get Bluetooth symbol on upper left corner of screen ( at least that's what it did on 9640 )
That Bluetooth adaptor only works with 9620, 9620C, 9621G, 9630, 9630G, 9640, 9640G, 9650, and 9650C
The 9641G does have Bluetooth capability built in.
So no dice with the 1616/16xx IP Phones.
Andre