You can only disconnect the incoming cable into the master socket and repurpose it and any extension sockets wired from it if FTTP has been installed and the copper pair is effectively redundant…..for someone on FTTC where the incoming pair is still in use with the broadband service , the extension cable to the first extension socket needs to be isolated from the master socket , then at a convenient point an extension socket connected to the telephone port on the router ,
a link has been provided with details , or search voice re-injection …as extension sockets should be wired in series, connecting the nearest socket to the router should make all sockets ‘live’ , provided the entire extension network is isolated from the master socket first , obviously without disturbing the router connection to the master socket ,assuming the router is connected at the master socket.
