I just noticed in the brochure image this also has a "Emergency" button.

Scrolling downward into the brochure I see a bullet point for:

• This telephone (single line telephone) can be used by connecting it to a Panasonic PBX (KX-TE, TDA, TDE, NCP series).

"Most people don't have a sense of humor. They think they do, but they don't." --Jonathan Winters