What Full Fibre (FTTP) Means for Your Business Phone Lines

Quick answer

There is no phone line on full fibre. An FTTP circuit is a data connection and nothing else - no dial tone at the wall socket, no analogue signal, no copper pair. Your calls instead run over the fibre as a voice service, and your existing number ports across unchanged. The install is straightforward; what catches businesses out is everything around it - the extension sockets that stop working, the copper line that must stay alive until the number has moved, and the alarm or lift that was quietly using the old line.

Full fibre is a genuine upgrade, and it is where most UK businesses will end up. But it arrives as a broadband product, sold by broadband people, on a broadband order form - and the phone consequences are rarely spelled out on that form. If you want the phone side planned alongside the install, get a no-obligation quote and we will sequence both.

Why there is no phone line on full fibre

On the old network one copper pair did two jobs at once: it carried a voice signal from the exchange, and - once broadband existed - data in the frequencies above the voice band. That is why an ADSL or FTTC connection always came with a phone line underneath it, whether you wanted one or not.

Full fibre replaces that copper pair with a glass fibre terminating in a small box on your wall called an ONT (optical network terminal), which hands you an Ethernet port. There is no voice band, no exchange battery feeding a dial tone, and nothing for an analogue handset to plug into. That is the design, not an omission, and it is the same direction of travel as the PSTN switch-off retiring copper voice on 31 January 2027. For the connection itself - speeds, availability, how it compares with older broadband - see our guide to FTTP and full fibre.

What actually lands in your building on install day

The row that matters most is the ONT. Its position is decided at survey and it is awkward and chargeable to move afterwards. If the engineer terminates by the front door because that is where the copper came in, your router lives by the front door and everything else has to reach it. Ten minutes on the phone before the survey beats any amount of rework after it.

Where your calls go instead

On FTTP, voice becomes a service you buy rather than a property of the line. It usually takes one of three shapes: a single digital line for one phone, a hosted phone system for a team, or SIP capacity feeding a phone system you already own. Which fits depends on how many people answer calls and what equipment you already have, and we compare the options with a decision table in business landline alternatives. This page assumes you have made that choice and are planning the install around it.

Worth knowing here: call quality on full fibre is rarely the problem. When calls sound poor on FTTP the cause is almost always the local network, the handsets or the router configuration rather than the fibre - see common VoIP problems and fixes.

Who arranges what

The last two rows are where FTTP projects go wrong. No order form asks about your alarm panel and no broadband engineer will notice one. Start with devices that rely on phone lines, and make those calls before the install date.

The overlap that protects your number

The most valuable thing in this guide is the order of work. FTTP install and copper cease are separate orders placed with separate teams, and nothing interlocks them.

1. Order FTTP. Do not cancel anything yet.
2. Order the voice service to be ready on the same connection.
3. Let FTTP install and prove it works - speed, upload, and a test call on the new service using a temporary number.
4. Port the numbers from the old copper line to the new voice service on an agreed date.
5. Test everything again on the ported numbers, including inbound from an outside mobile.
6. Only now cease the copper line.

Illustratively, that means paying for the old line and the new connection together for perhaps four to six weeks. People try to compress it to save a month of rental, and it is the wrong economy: cease the copper before the port completes and the number returns to the outgoing provider's pool, where recovering it is slow, uncertain and occasionally impossible. One month of legacy rental against your main business number is not a close call - and that rental has risen through 2026 anyway, as covered in the WLR price rises.

The part that catches people out: your extension wiring

In most older buildings, one master socket fed a spider's web of extension sockets - reception, the back office, the warehouse phone by the door. All of it is analogue wiring hanging off a copper pair, and on FTTP it is dead cable. Nothing surprises people more on day one.

There are three honest ways to get phones back to desks. IP handsets on your data network plug into the same structured cabling as your computers, ideally on a switch providing power over Ethernet - tidiest if the building already has data points where phones need to be, most expensive if it does not. DECT puts a cordless base station near the router with handsets around the building and avoids cabling entirely, which suits warehouses, workshops and older premises; coverage and repeater limits are worth checking before you buy. An adapter near the router lets you keep one specific existing phone, but it does not re-energise the extension sockets, so that handset has to live by the router.

There is a fourth option people reach for and should not: back-feeding your old extension wiring from the router's phone port. It sometimes appears to work, it can interfere with the master socket and anything else on that wiring, and no reputable installer will sign it off.

What to check on the connection itself

Full fibre is fast enough for voice many times over, but three specifics are worth confirming rather than assuming:

• Upload speed. Calls use upload as much as download. Most business FTTP packages are generous, but some consumer-grade tiers are not symmetrical, and upload is what carries your voice out.
• Headroom under load. A call competing with a large cloud backup on a busy afternoon is where quality problems appear. Our guide to internet speed for VoIP sets out what to size for.
• What happens when it fails. One connection now carries phones, data and possibly card payments. That concentration is the argument for 4G or 5G failover.

FTTP or SoGEA, and what full fibre does not solve

If full fibre is not yet available at your address, SoGEA does the same job over the existing infrastructure and voice works identically on it. Choosing between them where both exist is a real decision with cost, speed and lead-time trade-offs, and we work through it in SoGEA vs FTTP for business. The phone-side planning is the same either way - including two things the upgrade does not fix.

Power. Copper carried a trickle of power from the exchange, which is why a corded phone worked in a blackout. The ONT, router and handsets all need mains power. A small uninterruptible power supply plus automatic diversion to mobiles covers the common cases - see landline resilience and failover.

Everything that was not a phone. Alarm signalling, lift emergency lines, card terminals, door entry panels and telecare each need their own migration, arranged with whoever maintains them. They carry the longest lead times in the project.

The bottom line

Full fibre has no phone line in it, and that is the design rather than a gap. Your calls move onto the connection, your numbers come with you, and day to day almost nothing changes for the person answering the phone. What needs planning is the physical reality: where the ONT goes, how handsets reach desks once the extension wiring is dead, keeping the copper alive until the number has moved, and the devices that were never phones at all.

If you would rather not discover the extension wiring problem on install day, tell us what the building looks like and we will plan the fibre and the phones as one job: get a no-obligation quote or call 0333 006 9399.

Getting unknown calls on a business line? Our free UK phone number checker shows which network or provider Ofcom allocated any number to, and whether the range is in service — no sign-up.