Quick answer
Digital Voice is a single phone line delivered over your internet connection instead of a copper pair. The handset plugs into the router rather than the wall socket, you keep your number, and to whoever answers the phone it behaves much as before. It is the closest thing to a like-for-like swap for a traditional line, and for a shop, a micro-business or a simple back-office phone it is often the whole answer. It is also genuinely limited: one number, one phone, no routing, no reporting, and no dial tone when the power is off.
This guide explains what a digital line actually is, what changes on the day it goes in, and where it stops being the right product. It deliberately does not try to talk you into or out of it against the other options - that comparison lives in business landline alternatives. If you want a straight answer on whether a digital line fits your setup, get a no-obligation quote and we will tell you.
What Digital Voice actually is
Strip away the marketing and a digital line is simple: your provider gives you a phone service that arrives as data over your broadband, and a device - usually the router itself - converts it back into something an ordinary telephone understands. Lift the handset and you get a dial tone. Dial a number and it rings.
Under the bonnet it is the same principle as VoIP, which is why the terms get muddled. The distinction worth holding onto is one of scope rather than technology. A digital line replaces a line. A hosted phone system replaces a phone system. Both carry voice as data; only one of them can route a call to whoever is free.
There is a naming problem here that causes real confusion. "Digital Voice" is BT's brand, but the same product is sold as a digital line, a digital phone line, single-line VoIP, a broadband phone line or simply "your new phone service" depending on who you buy it from. None of those names tells you what you are getting. Compare the specification - how many simultaneous calls, which features are included, what happens in an outage - not the label.
What changes and what does not
| Traditional analogue line | Digital line | |
|---|---|---|
| Where the phone plugs in | Wall socket | Router, or an adapter connected to it |
| Your number | Yours | Same number, ported across |
| Dial tone and dialling | Normal | Normal |
| Power in an outage | Line carried its own power | Stops unless you have battery backup |
| Extension sockets around the building | Work | Dead - only the router position is live |
| Call quality | Fixed by the copper | Depends on your connection, usually better |
| Features such as divert and caller display | Often chargeable extras | Usually included |
| Simultaneous calls | One per line | One, unless you buy more |
| Broadband | Rode on the same pair | Separate product the line depends on |
Two rows in that table cause almost all of the surprises. The extension sockets row catches out anyone in a building with phones in more than one room: that internal wiring hangs off the old copper pair and stops working with it, so a phone in the back office needs either a cordless handset, a data point, or the router moving. The power row is the one everybody has heard about and few actually plan for.
Plugging in: the three ways it arrives
Straight into the router. Most business routers now have a telephone socket on the back. Plug your existing corded or cordless phone into it and you are done. This is the common case and it takes about a minute.
Through an analogue telephone adapter. A small box that sits on your network and provides a phone socket. Useful when the router has no phone port, when the phone needs to be somewhere the router is not, or when you want to keep a particular handset.
As an IP handset. A phone that speaks the protocol natively and plugs into a data point. Not really a "digital line" any more so much as the first step towards a phone system, but it is what many providers ship.
The differences that actually matter day to day
Most of the time nothing feels different, which is the point. Four things do.
It depends on your internet. Not just on it working, but on it having room. A single call needs very little bandwidth, but it needs that bandwidth consistently while somebody else is uploading a large file. Our guide to internet speed for VoIP covers what to check.
It depends on mains power. Copper carried a small current from the exchange, which is why a corded phone worked in a blackout. Nothing in a digital setup does. A small uninterruptible power supply on the router, plus an automatic divert to a mobile, closes this gap for well under the cost of a lost afternoon - see landline resilience and failover.
Short codes may behave differently. 1471, 141, 1470 and 1571 are exchange features on the old network. Most providers reproduce them, some reproduce them differently, and a few replace them with an app or a web portal instead. Ask specifically if you rely on one - our guide to landline calling features maps the whole set across.
Faxes, modems and anything that whistles down the line will not work reliably. Digital lines compress voice, and compression that is imperceptible to a human ear is fatal to a fax handshake. See fax after the switch-off.
Emergency calls: the honest position
999 and 112 work normally from a digital line. Two caveats are worth stating plainly rather than burying.
First, they do not work in a power cut, because nothing in the chain is powered. Ofcom's protections in this area are written around residential and vulnerable customers rather than businesses, so do not assume a battery back-up unit will be offered with a business line - ask. In practice the realistic answer for most businesses is a charged mobile and a UPS.
Second, the address matters. On copper, the emergency operator could rely on the line's physical location. A digital service can in principle be used anywhere there is internet, so the address registered against the service is what gets passed. Check it is right when the service goes live, and update it if you move a handset to another site.
What to check before you order
- Confirm the connection it will run on, and its upload speed as well as download.
- Ask how many simultaneous calls are included, and what a second costs.
- Confirm your number will port, and that the old line stays live until it has.
- List the features you actually use today and check each one by name.
- Ask what happens in a power cut, and whether backup is offered or your responsibility.
- Work out where the phone needs to physically be, given the router position.
- Check the emergency-services address held against the service.
- Confirm nothing else is sharing the old line - alarm, lift, card terminal, gate intercom.
That last item is the one that turns a simple job into an incident. Before you order anything, walk the building with devices that rely on phone lines open.
Where a digital line fits, and where it does not
| Your situation | Digital line? | Why |
|---|---|---|
| One phone, one person, one number | Yes | Cheapest, familiar, nothing to learn |
| Shop or salon with a single counter phone | Yes | Behaves like the line it replaces |
| A back-office or secondary number | Yes | Provided nothing else uses that line |
| Two people needing to answer the same number | No | You need shared answering, not a second line |
| Calls routed by department, or a queue | No | A digital line has no routing |
| Anyone wanting missed-call reporting | No | There is nothing to report from |
| An existing on-site phone system | No | That wants SIP capacity, not a single line |
| An alarm, lift, telecare unit or dial-up card terminal | Never | Each needs its own replacement |
If you land in the "no" half of that table, the honest next step is the comparison rather than a workaround. We set out all five replacement routes, with prices and a decision table, in business landline alternatives, and map line roles to replacements in analogue line replacement options.
The bottom line
A digital line is the least dramatic way to leave copper behind: same handset, same number, same habits, plugged in somewhere slightly different. For a single phone that is genuinely all most businesses need, and paying for more would be waste. Just go in knowing the three real changes - power, internet and dead extension sockets - and knowing that a digital line cannot share a call between two people, because that limit is where most regret starts.
Not sure whether one line is enough? Tell us how many people answer the phone and what else is plugged into your old line, and we will say plainly which product you need: 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.
Frequently asked questions
What is Digital Voice?
A phone line delivered over your internet connection rather than the copper network. The handset plugs into the router or a small adapter, you keep your existing number, and day to day it behaves much like a traditional line - with the differences being power, internet dependence and the loss of your extension sockets.
Is Digital Voice the same as VoIP?
It uses the same underlying technology, but the scope is different. "Digital Voice" and similar names describe a single-line, like-for-like landline replacement. VoIP or hosted telephony describes a full phone system with multiple users, call routing, direct numbers and reporting.
Will Digital Voice work in a power cut?
No, not by default. The router and any adapter need mains power, and the connection needs to be up. A small UPS covers short outages and an automatic divert to a mobile covers longer ones. Emergency calls are affected too, so keep a charged mobile to hand.
Can I keep my number with a digital line?
Yes. Your existing geographic number ports to the digital service and customers carry on dialling the same thing. Make sure the old line is not ceased until the port has completed - that sequence matters more than any other detail in the move.
Can I plug my old phone into a digital line?
Usually yes. Ordinary corded and cordless phones work either in the router's telephone socket or through an analogue telephone adapter. What will not work reliably is anything that sends tones rather than speech, such as a fax machine, a modem or an old dial-up card terminal.
Will my other phone sockets around the building still work?
No. Those extension sockets are wired to the old copper pair and stop working with it. Your options are a cordless phone with the base by the router, an IP handset on a data point, or moving the router. Work this out before install day rather than after.
Is a digital line enough for a small team?
Only if one person answers the phone at a time and nobody needs to pick up for anyone else. As soon as calls need to hunt between people, queue at busy times, or route by department, a single digital line cannot do it and a hosted phone system is the right product instead.