I have tried connecting the cord to the Viking, both in "Line In" and "Phone". Neither works.

As I said before, the Viking tech said the "Line In" should not be used with a phone system, only the "Phones" outlet. But I've tried a line cord from the Viking "Phones" outlet to slots 37-47 with no success.

There is a ringing at both Viking intercoms (door and gate) when the buttons are pressed; it just doesn't ring into the phone system.