Not all expansion modules are key based, but it is common in CS 1000 terminology to use Key Expansion Module as a phrase to indicate any type of expansion module.

An expansion module is a modular unit with different numbers of keys or touch-sensitive areas on a screen that are based on the specific expansion module. A module that is designed to provide expansion capabilities to a specific station type can be attached to 16-key 2xxx digital phones, specific 39xx digital phones, and most UNIStim IP phones. Note that an expansion module is specific to at most a family and cannot be used with others. For example, to all two column digital stations.

Depending on the history, a specific station may have more than one possible choice of key expansion module. On the other hand, some modules are limited to a subset of the stations in the family having the capability of supporting the added modules. Module A may be usable by a superset, including a subset of the endpoints that support module B.

The modules provide a user with extra programmable keys. These extra keys can be assigned to any combination of lines and features. You can typically add more than one expansion modules to a single telephone. Thereby, increasing the in line/feature keys. However, in all cases there will be a finite limit on the number of permitted extra buttons.

The expansion module usually needs a separate base for the modules. They do not use the same base as the station itself.

The Key Expansion Module connects to the telephone through a ribbon cable running from the base of the telephone. It is physically connected to the telephone by the base, which attaches to the base of the station.

The expansion module requires additional power.

For more information, see Key Expansion Modules in Appendix G: Generic station operations.