Thanks; I got the voicemail working: From the Panasonic's web interface, on the TELEPHONE tab, click on call control, line 1 and enter "123" (without the quotes ) for the Voice Mail Access Number.
Still interested in your notes, as I am not sure I have my settings right. The biggest pain with the Panasonic is setting the registration interval down to 10 minutes (600) which requires a TFTP provided configuration file as it cannot be set through the web interface. I've had to reboot and re-provision with the file about a hundred times before it actually took!