BT Business Total Broadband Fibre User Manual page 51

Landline cable (optional)
With the landline cable fitted:
you can make calls using your business telephone number from the phone that's
•
plugged into your Fibre Hub by dialling '5' before the number you wish to call.
If you don't dial '5', you'll make the call using BT Business Broadband Voice
the phone plugged into your Fibre Hub will automatically use your main
•
telephone line to make outgoing calls if there's a power cut or broadband
service failure
Plug the purple connector into the purple landline socket on the back of your
Fibre Hub and plug the other end of the cable into the telephone socket on your
master socket or a telephone extension socket.
Your Fibre Hub and Openreach modem 49