Hi Stevie,

A little late on this, so I'm guessing you've probably solved the problem already, but the Panasonic proprietary phones just need a connection via a regular BT431A plug.

Voice pair (3/4 on PBX modular jack) goes to LJU terminals 2/5, data pair (2/5 on PBX jack) to LJU terminals 3/4.

The LJU needs to be a secondary jack WITHOUT capacitor, of course.