... to configure a router that usually the majority of them does not have the VoIP system on board, you have to get an external system called VoIP - ATA, there are several models (Cisco, Linksys, Grandstream, Gigaset and many others!) For sale Even on Amazon or other telecommunications devices vendors, usually those for home are found with two fxs outputs (so two VoIP lines) if you want 4 or more (in this case you already start talking about VoIP switches) the price obviously salt And a lot and also the complexity of the configuration, certainly not to everyone's reach, my advice and to turn to some of your friends who know how to handle ata-voip systems, because there is really to lose your head in configuration if You do not know all the RFC parameters. (Which are many, and change from country to country!) Otherwise to simplify things, you can buy a DECT VoIP Gigaset phone because the Gigaset configuration is not as complex as the ATA (if for sale in your country!) Usually allows you to Configure up to 6 ISP VoIPs and 6 portable telephones with a single transmission base and solve the problem faster and at a lower cost of the ATA-VoIPs if only 1 phone and its base so you get 100mt at home and 300 in the open field DECT-VOIP coverage. (I will clarify that they are not a product vendors mentioned, I have nothing to do with the companies above, but it is only a personal experience of use of common user or customer!)