Analog display services interface

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.

The technology introduced in the United States and rolled out to Regional Bell Operating Companies (RBOCs) from Bellcore in April 1995, (very soon after the introduction of CLASS-based services through electronic switching system (ESS)), was marketed by the RBOCs who implemented it, as a way to streamline all available custom calling options through the use of a screen-based telephone; giving residential and small business telephone subscribers PBX-like functionality at home or in small office/home office (SOHO) locations at a significantly lower cost.

This greatly increases customer usability by alleviating the need to memorize dialing codes such as *69.

Nortel discontinued the x5x telephone line and introduced a more streamlined version called the 39x-line and then later the 48x-line in 1998.

CIDCo and Cybiotronics later introduced their own lines of screenphones after the original Nortel Patent expired.