An Off-Premises Extension (OPX) is a dedicated circuit connecting a distant location to a main PBX to provide the same phone system features available at the main location. Answering services, small businesses and people working from a home or remote office often use these circuits.

This service is not specific to any vertical market. Off-Premises Extensions are used by practically all types of business and are available locally as well as nationally. Off-Premises Extensions are sometimes referred to as Off-Premises Station (OPS).