Voice over Internet Protocol (VoIP) private network call rerouting or switching, substantially transparent to both the caller and the called party. IP private network calls (e.g., VoIP private network) are automatically switched over a Public Services Telephone Network (PSTN) such as an Integrated Services Digital Network (ISDN) as the need arises. Alternate routing may occur because of, for example, network congestion, network outages, or detected poor Quality of Service (QoS) in the private network. Routing is over existing customer PSTN trunks and a dedicated Direct Inward Dial (DID) number, unlisted, that serves all users at a distributed system. Calls that may be switched to the PSTN (ISDN) are correlated with call associated information, such as a private calling user number, name, classmarks, Dialed Number Identification Services (DNIS), user group. VoIP calls made between users appear as intranetwork calls regardless of whether they are intranetwork calls or alternately routed.