A firewall configured to be interfaced between an internal and an external networks. The firewall includes a VoIP processor for detecting an outgoing VoIP packet sent from the internal network, for changing data in a header of the VoIP packet and also changing data contents in the VoIP packet corresponding to data changed in the header to enable bi-directional VoIP communication. In one embodiment, the VoIP processor changes a source IP address and a port number in the header of the VoIP packet and also changes the data contents in the VoIP packet corresponding to the source IP address and the port number changed in the header to enable bi-directional VoIP communication. In another embodiment, the firewall further includes an external VoIP interface comprising multiple VoIP ports for receiving multiple incoming VoIP packets each designated with one of the VoIP ports. And, the VoIP processor further includes a VoIP port versus internal address table for identifying an internal address in the internal network for directing each of the incoming VoIP packets to the internal address identified.