The traditional phone line that carries voice as an electrical signal over copper wires. This is the system being retired. Also called a PSTN line.
Broadband router (hub)
The box in your home that connects you to the internet. On digital voice, your phone also connects through this box. Sometimes called a home hub or wireless router.
Digital voice
The replacement for the analogue phone service. Your voice is converted to data and sent over your broadband connection. Also called VoIP or IP voice. Your phone number does not change.
DTMF (Dual-Tone Multi-Frequency)
The tones produced when you press numbers on a phone keypad. Some devices (like door entry systems) use these tones to trigger actions. DTMF can be unreliable over digital voice.
FTTP (Fibre to the Premises)
A broadband connection where fibre-optic cable runs all the way to your home. Also called full fibre. Requires an ONT box where the fibre enters the building.
FTTC (Fibre to the Cabinet)
A broadband connection where fibre runs to the green street cabinet, and the final stretch to your home uses the existing copper phone line. Slower than FTTP but more widely available.
ISDN (Integrated Services Digital Network)
A digital phone system used mainly by businesses for multiple phone lines. ISDN is also being retired as part of the switch-off.
ONT (Optical Network Terminal)
A small box installed where the fibre cable enters your home on an FTTP connection. It converts the light signal from the fibre into an electrical signal the router can use. It needs mains power.
Openreach
The company that maintains the physical phone and broadband network used by most UK providers (BT, Sky, TalkTalk, Plusnet, and others). Openreach is part of the BT Group but operates separately from BT's retail arm.
Priority Services Register (PSR)
A free service offered by phone providers and energy companies. If you are elderly, disabled, chronically ill, or in another vulnerable situation, being on the register means you get extra support during outages and service changes.
PSTN (Public Switched Telephone Network)
Public Switched Telephone Network. The digital switching system built in the 1980s to route calls across the UK's copper phone network. Often used as shorthand for the whole analogue landline system. The PSTN and the copper lines it runs on are being switched off by January 2027.
SIP (Session Initiation Protocol)
A standard used to set up voice calls over the internet. SIP trunks are the business equivalent of a digital voice line, replacing ISDN and analogue trunk lines.
Stop sell
The point at which a provider stops selling new analogue phone services in an area. After stop sell, new customers get digital voice. Existing customers keep their analogue line until it is individually migrated.
Telecare
Technology that monitors people at home and can call for help automatically. Includes pendant alarms, fall detectors, epilepsy monitors, and bed sensors. Many telecare devices connect via the phone line.
UPS (Uninterruptible Power Supply)
A battery device that provides backup power when the mains supply fails. A mini UPS can keep a broadband router running for several hours during a power cut.
VoIP (Voice over Internet Protocol)
The technology behind digital voice. Voice is converted to data packets and sent over the internet. See digital voice.