Abstract: Customers that have groups of stations served from multiple digital switching systems, which frequently include mixtures of PBXs and Centrex, require capabilities that will allow those station groups to operate as one global group. This invention permits customer station groups, including PBXs and Centrexes interconnected by private facilities or by the public switched telephone network (including long distance carriers), to act as a single entity that supports integrated voice and data communications. Advantageously, Integrated Services Digital Network (ISDN) Primary Rate Interface (PRI) facilities are used to carry the communications and signaling to and from the PBXs.