A method and apparatus for protocol conversion using channel associated signaling (CAS) is disclosed. A protocol conversion system is located logically between a first signaling system and a second signaling system, in which the first signaling system uses the Common Channel Signaling (CCS) protocol and the second signaling system uses CAS, which is incompatible with CCS. The protocol conversion system receives a first message from the first signaling system that conforms to the CCS protocol, converts the first message to one or more second messages that conform to the CAS protocol, and communicates the one or more second messages to the second signaling system, whereby a voice conversation is established between the first signaling system and the second signaling system. The protocol conversion system preferably comprises a universal protocol converter coupled to a CAS module. The CAS module interfaces trunks of the two incompatible networks and drops or inserts signaling information in frames carried by the trunks. The universal protocol converter executes a state machine that determines how to convert CCS messages into CAS messages, and instructs the CAS module what messages are to be sent to each network. In this configuration, voice conversations can be set up over incompatible signaling networks.