A telephone socket is the main socket where the BT Cable enters the building, also known as a "master socket" or a NTE5 socket, it provides a clear demarcation between network and customer wiring. This is what you will be asked to use to identify any line faults. It is also the most popular place for your router as this is where it will pick up the best broadband speed.There are different types of face plates on the sockets some are split and able to remove with a screwdriver and the more modern versions are clipped so no screwdriver is needed.