Analog display services interface

Analog display services interface (ADSI) is a telephony technology that is used in plain old telephone service (POTS) or computer-based private branch exchange (PBX) telephone service. It works in conjunction with a screen-based telephone ("screenphone") or other compatible customer-premises equipment (CPE) to provide the user with soft key access to telephone company or internal PBX custom calling features.

Source: Wikipedia — Analog display services interface (CC BY-SA 4.0)