Models 58205821 voice over ip telephone adapters allow standard analog telephones to make and receive calls over a broadband internet connection both models have two fxs ports to allow two voip channels simply plug one or two conventional or cordless phones into a model 5820 or 5821 and then plug the telephone adapter into a broadband connected router or internet gateway a minimum of five attached phones can be rung simultaneously on each fxs port using the built in ring generator t