VoIP vs Landline: The Best Choice for UK Small Businesses

What is happening, and by when

The old network carries calls over copper wires from the local exchange. It is being replaced by calls carried as data over a broadband connection. Openreach says the retirement covers all services that rely on the copper phone network, including ISDN lines and ADSL and FTTC broadband.

So if your office still has an ISDN phone system, or broadband that arrived with a phone line rental, this affects you even if you rarely use the desk phone.

What doesn't change

• Your phone number. Ofcom says landline customers keep their numbers when their line moves to digital, and you have a legal right to take your number to another provider (porting). Your new provider handles the port.
• How you dial. People still call the same 01, 02 or 03 number, and you still dial out the same way.
• Your handsets, often. On a Digital Voice-style service, a standard phone usually plugs into the broadband router instead of the wall socket, as Ofcom explains.

Digital Voice vs a full VoIP system

Both are VoIP, meaning calls travel over the internet. The difference is how much changes.

Digital Voice (the name BT and several other providers use) is the like-for-like swap. You keep one line and one number, and plug your phone into the router. It suits a small shop or a sole trader who just wants the phone to keep working.

A hosted VoIP system (also called a cloud phone system) replaces the line altogether. You get numbers, users and extensions in an online portal, with apps for mobile and desktop. You can take calls on your office number from anywhere, set up call queues and ring groups, and change routing yourself. It suits teams, several sites, or anyone who works away from the office.

Costs for either depend on the number of users, whether you need new handsets, your call bundle and contract length. Get written quotes on the same basis before comparing.

Landline vs Digital Voice vs VoIP at a glance

On power cuts: BT confirms its router must have power for Digital Voice calls. Ofcom requires providers to offer anyone who depends on their landline a way to reach 999 in a power cut, such as a battery backup.

Checklist: kit that may use your phone line

Phones are the easy part. The risk is equipment that quietly dials out over a copper line. Walk round the premises and note anything plugged into a phone socket. BT and Openreach both flag these:

• Intruder and fire alarms that call a monitoring centre.
• Card payment terminals that connect through a phone line.
• Lift emergency phones.
• Telecare and personal alarms for staff or residents.
• Door entry systems and CCTV that dial out.

Also check anything else on a phone socket, such as a fax or an older franking machine. For each item, ask its supplier whether it works on a digital line or needs an upgrade, and get the answer in writing.

Questions to ask a provider

1. Can you port my existing number, and what happens to calls on the day it moves?
2. What is the minimum contract term and the notice period?
3. What is included in the call bundle, and what do calls to mobiles and 03 numbers cost?
4. Do I need new handsets or a new router, and who pays for them?
5. What happens in a power cut or broadband outage? Is battery backup or mobile failover available?
6. Can I set call forwarding and failover myself, or do I have to ask support?
7. Will my alarm, card terminal or lift line work on your service?
8. Is UK-based support included, and during what hours?

How call diverts work on each

Landline and Digital Voice: diverts are usually set with star codes from the handset, or in your provider's online account. Our guide to diverting BT calls walks through the codes.

Hosted VoIP: log in to the provider's portal and set forwarding on the number or user. Depending on the provider, you can forward every call, forward after a set number of rings, or forward only out of hours. Look for a failover or continuity setting too. It sends calls to another number if your office is offline, for example during a broadband outage.

Mobiles: see our iPhone and Android forwarding guides.

Frequently asked questions

Will I lose my business number?

No. Moving to Digital Voice keeps your number, and you have a legal right to port it to another provider. Don't cancel your old line before the new provider has completed the port.

Do I have to switch before 31 January 2027?

Yes, if you're still on an analogue line or ISDN. Your provider should contact you, but moving early gives you time to test alarms and card terminals.

Will my phone work in a power cut?

Not on its own. A digital line needs the router to have power. Ask about battery backup, and keep a charged mobile as a fallback.

Is VoIP always the better choice?

Not always. If you have one line and no plans to change how you work, Digital Voice is simpler. If you need extensions, several sites, or calls on your mobile, a hosted system gives you more control.