the 1st pic is your PHONE SOCKET. a MASTER SOCKET is the first socket where the phoneline is. the PHONESOCKET above has a test socket inside of it. the purpose of the test socket is to bypass any extension socket in your house. if your bb works on the test socket definitely theres a fault on the initial socket. you need to ring bt faults and let them fix it for you. a PREFILTERED SOCKET is a socket with two-holes (not a splitter plugged into it) it doesnt need a filter.