First I would confirm what the 4th button is programmed as on the phones by pressing the function or feature key and the 4th button, if CO 04 or Trk 04 comes up you have a bad trunk port.
If it comes up as something else the button will need to be programmed as a trunk key.

This is not a simple thing to do, there will be multiple programming steps to take per phone in the systems main programming.
Have you tried the local NEC dealer or reseller for help?


We get old too soon, smart too late