Conveniently, connecting an analog terminal to a router to use an IP phone connection

Since there are 2-, 4- and 6-pole cable of this type, I wondered only that well for connecting an analog terminal (in my case, a Brother fax, an analog phone but is the same) with a router (in my case a Fritzbox that both TAE and alternatively Western jacks has) is required to use an IP telephone. This 4-pin cable is working properly.