What should happen is the installer should put the ntl socket next to the bt master .When you had the install the tech should of asked you if you had telephone exts then he would find the master socket as this is normally where the exts are fed from.Then the tech should transfer the exts from the bt socket to the ntl socket .The only socket left on a bt line should be the master this is incase you decide to go back to bt you have a line ready to go The wiring code is as follows Blue cable with white stipe 2 orange cable with white stripe 3 white cable with blue stripe 5 hope this helps