A system for verifying VoIP call routing information. The system may include an apparatus integrated with a private branch exchange (PBX). The apparatus may store at least one call attribute of a public switched telephone network (PSTN) call initiated to a destination telephone number. The apparatus may verify a destination Voice-over-Internet-Protocol (VoIP) call agent for the destination telephone number based on demonstrated knowledge of the PSTN call. The apparatus may route a new call either over a VoIP network to the destination VoIP call agent or over a circuit switched network based on whether the destination VoIP call agent is verified for the destination telephone number.