This invention relates to a supplementary services layer (SSL) application (200) in the switching node (32) for the development and execution of subscriber-based supplementary services. The SSL communicates with the L4 application (36) through an L4-L5 interface (240). Therefore, a system operator may configure the switching node (32) to execute supplementary services without intervention from a host application and without modification to the current L4 application. The SSL also communicates with the L5 application in order for that application to integrate supplementary services without further modifications. The SSL comprises a Database Interface Service (202), a Service Object Manager (SOM) (204) and one or more instances of a Supplementary Service Object (SSO) (206; 208). The database interface service (202) provides connection to an external database which stores each subscriber's profile. Each SSO instance (206; 208) implements one or more supplementary services for a call. The SOM (204) exercices overall control over these SSO instances (206; 208).