An end office (102) of the PSTN (101), which employs independent switching networks (142, 152) which share one or more office codes, is served by a single assigned node (105), screens all incoming call messages (191) (IAM)'s; directs messages which include an appropriate Channel Identification Code (CIC) to the switching network that serves that CIC; rejects messages that include an improper CIC; and requests that the calling office assign a different CIC to the incoming call. In an alternate configuration, a signaling message intercept unit (512) is interposed between a signal transfer point (108) (STP) and end switches (103, 104), to determine which of two or more switches should receive a message, based on the directory number, a circuit identifier or a message index of the received message, and forwards the message to the correct switch.