One of our field offices has a number of analog phones, with older headsets. I haven't seen one in person, but the people there told me it's a "Avaya/Plantronics KS23822-L1". I think it's made by Plantronics, but sold by Avaya. Other websites seem to indicate the Avaya part number is 406741900
I checked both companies websites, and can't find much info.
Does anybody happen to know if this headset would be compatible with the Cisco 7965G? I realize it wouldn't support Headset Hookswitch Control, which is fine..just wanted to see if it'll work as it does today for them.
The plug end on the Headset Cord is the standard quick-disconnect cord with RJ-12 (modular) adapter (same as your handset jack).
The determination between Handset/Headset is via the Headset Button on the 7965 itself.
If you have a look at this tutorial for the 7941 (sorry I don't think there is one out for the 79x5 series yet) you will see the Button described and shown quite nicely :)
Hope this helps!