PSTN to VoIP solutions such as VoIP Gateways, Telephony Interface Cards, and Channel Banks are needed to bridge VoIP networks and equipment to traditional telephone networks and equipment such analog POTS lines, digital voice T1's, legacy PBX's, and the normal Public Switched Telephone Network (PSTN). These devices can range from a simple VoIP adapter that has a single conventional telephone port and a single ethernet port to multi-port T1 VoIP media gateways, internal server based PCI telephony cards, or Channel Banks.
Most often, PSTN to VoIP solutions are used in conjunction with VoIP business phone systems, which will typically include a PSTN to VoIP interface device to allow the system to make calls to the PSTN. In other cases, a PSTN to VoIP Solution such as a VoIP Gateway will be used to connect remote branch offices that have legacy PBX's together over a data network to help reduce long distance costs.