What's the cable called from the TEL 1 port on the open reach fibre modem to the primary socket to link all the phone sockets in a new build property?
Do you have a link to where I can buy one please
Look on Amazon for "kenable BT 4 Wire 431A Plug to 4 Wire Male Plug Telephone Cable Lead 1m White"
Or on the Kenable Website "BT 4 Wire 431A Plug to 4 Wire Male Plug Telephone Cable Lead 2m White"
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Your developer should have left a suitable cable when the ONT was fitted.