Well,.. with the weather we had rip through Kentucky this past week (TS / TD Helene) Didn't get to circle back to this, but discovered one possible issue. the Headset button on the phone itself needed to be enabled. (duh)
Yes, when I test this with another phone (T46p) and my Jabra headset, the headset doesn't ring when dialed. Checked to ensure that phone was enabled on the Jabra - but didn't seem to make a difference.
I expect it is something simple,.. and easy to overlook, but not found it yet. And today I am trying to not think about work and work on the 720,.. Curious as to what else I can end up putting on this as a Proxmox host.