A VoIP trunk gateway is an interface that facilitates the use of plain old telephone service (POTS) equipment, such as conventional phone sets and fax machines, with a voice over IP (VoIP) network.
Commercially manufactured VoIP trunk gateways take the form of self-contained units (boxes) or circuit cards. The number of ports for POTS devices varies, depending on the intended application (small business, medium-sized business, or enterprise). The VoIP trunk gateway connects subscribers to the VoIP network without involving operators or incurring telephone company toll charges. The VoIP service provider establishes its own schedule of rates, if applicable, for local and long-distance calling.