Supporting the ability to connect KX-TDA15/KX-TDA30 Hybrid IP PBXs to the growing list of SIP based Internet Telephony Service Providers (ITSP) to achieve low-cost VOIP calls over broadband IP network.  The SIP-GW4 comes with 4 port SIP trunk support which can be increased further to 8-ports by installing the optional SIP-DSP4 (KX-TDA3451 module. Each port on the SIP gateway card supports 1 bi-directional voice communication. The SIP gateway card also supports web programming for easy programming and configuration.