Why we wrote this

Almost every week we get the same call. “Our phone system is up for renewal, someone has told us the lines are being switched off, and we don’t know whether VoIP is right for us.” The answer is not the one most telecoms websites give. VoIP is right for the overwhelming majority of UK businesses, but when you move, what you move onto and what else is plugged into your old phone lines are the decisions that actually determine whether the switch goes well.

This guide is written from the installation van, not the brochure. It is based on 30 years of fitting and supporting business phone systems across the UK.

The short answer

VoIP is right for your business if all four of these are true:

• You have, or can get, a business broadband connection with a stable upload speed.
• You know what else is connected to your existing phone lines (alarms, lifts, door entry, card machines).
• Someone has thought about what happens to your phones in a power cut.
• You are willing to port your existing numbers rather than start again.

If any of those are unresolved, VoIP is still right; you are just not ready to switch yet. The rest of this article is how to resolve them.

The decision has already partly been made for you

The UK’s analogue phone network (PSTN and ISDN) is being retired. Openreach has already stopped selling new analogue and ISDN lines across the country, and the remaining services are being withdrawn in January 2027. In practice that means:

• You cannot order new analogue or ISDN lines for a new site, a new office or an expansion.
• Your existing lines will be migrated whether or not you plan for it.
• The only question left is whether you move on your timetable, with your requirements specified, or on someone else’s.

We cover the practicalities of the deadline on our ISDN switch off page. The important point for this decision: “should we move to VoIP?” has quietly become “when and how do we move to VoIP?”

The readiness test: 5 questions in this order

1. Is your internet connection good enough, and is it the upload that matters?

Most businesses check their download speed and assume they are fine. Calls are far more sensitive to upload, jitter and packet loss than to raw speed. As a working rule, a single concurrent VoIP call needs roughly 100kbps in each direction. Ten staff on the phone at once is around 1Mbps of upload: trivial on fibre, and a real problem on an old, contended copper line that also carries your cloud software, CCTV and backups.

What actually causes bad VoIP call quality in our experience, in order of frequency:

1. A contended or long copper broadband line (high jitter, not low speed).
2. A consumer-grade router with no quality-of-service handling.
3. Wi-Fi handsets or softphones on a saturated or badly covered wireless network.
4. An unmanaged switch daisy-chained across the building.

None of those are faults of VoIP itself, and all four are fixable before you migrate. If your connection is the weak link, sort that first with full fibre (FTTP), CityFibre or a leased line if you need guaranteed, uncontended bandwidth. If the building is the weak link, the fix is usually structured data cabling and properly designed business Wi-Fi, not a different phone platform.

2. What else is plugged into your phone lines?

This is the single most common cause of a migration going wrong, and it is almost never mentioned in “benefits of VoIP” articles. Analogue lines in UK commercial buildings very often carry more than voice:

• Intruder and fire alarm signalling (redcare-type and dialler-based)
• Lift emergency autodiallers (a legal safety requirement, and they must keep working)
• Door entry systems and gate intercoms
• Card payment terminals on a dial-up fallback
• Franking machines, fax lines and site-wide paging

Every one of these needs a decision before the line it sits on is ceased: replace with an IP or mobile-signalling equivalent, move it onto an analogue adaptor, or keep a single dedicated line for as long as one is available. A migration that only considers desk phones will take out a lift alarm at 5pm on a Friday.

3. What happens in a power cut?

A traditional analogue phone was powered down the line from the exchange and kept working when the building lost power. An IP handset does not, it depends on your switch, your router and your broadband. That is not a reason to avoid VoIP, it is a reason to specify around it. Practical options we fit:

• A UPS on the router, switch and any critical handset. An hour of resilience is the accepted benchmark for access to emergency services.
• Automatic failover of your main number to mobiles, which is configured in the platform and costs nothing extra.
• Mobile apps as the fallback, so an outage becomes an inconvenience rather than a closed business. See VoIP softphones.

Ask any provider what their power-cut answer is. If they do not have one, they have not installed enough phone systems.

4. How do your calls actually arrive, and where do people work?

The right platform depends far more on call flow than on headcount. Three patterns cover most UK SMEs:

• Reception-led: one main number, a person who answers and transfers visitors at a desk, wants a proper receptionist console and busy-lamp visibility, not just an app.
• Distributed / hybrid: staff split across home, site and office wants softphones and mobile apps with the same number and call history on every device.
• Volume-handling: sales, support, bookings wants queues, wallboards, call recording and CRM integration far more than it wants handsets.

Most bad phone system purchases come from buying the wrong pattern, not the wrong brand.

5. Are you keeping your numbers?

Yes, you can keep your existing geographic numbers when you move to VoIP, including 01604 and other local numbers, and you should. Porting takes planning and a few working days, and it is the one part of the project with a lead time you cannot compress. Never let a provider give you a “new temporary number” as a shortcut as your number is on vans, signage, Google and thousands of customer records.

Where VoIP genuinely saves money, and where it does not

Being straight about this matters more than a sales pitch. The savings are real but they are not where most people expect.

The honest summary: a five-person single-site office on a tight package will save a modest amount each month. A twelve-person business with hybrid staff, a second site and frequent starters and leavers will save materially, and most of that comes from the changes it no longer has to pay an engineer to make.

A worked example

A 14-person business across a main office and a small second premises, on ISDN2 channels, with a maintenance contract for a PBX in a cupboard. Staff take calls at home two days a week by diverting to mobiles, which loses the caller ID and means nobody can transfer a call.

Moving to hosted VoIP changed four things in practice: ISDN channel rental stopped; the two sites became one dial plan with free internal calls; home-working staff got the office number on a laptop and a mobile app so transfers worked again; and the diverts to personal mobiles (with the resulting invisible, unrecorded calls) stopped entirely. The phone bill fell, but the reason it was judged a success was that calls stopped going missing.

When VoIP is not the immediate answer

Three genuine cases, from experience:

• The connectivity isn’t there yet. A rural site on poor copper with no fibre date is a connectivity project first and a telephony project second. Fix the line, then move the phones.
• You have just invested in on-site kit. If a modern IP-capable PBX was installed recently, the right move is often SIP trunking: keep the system, replace the dying ISDN lines underneath it, migrate to hosted later when the hardware is genuinely end of life.
• The business is mid-move or mid-restructure. Migrating phones twice in a year is avoidable pain. Bridge on SIP, then do it once, properly.

Notice that in all three the answer is still “IP”; it is the hosted part that waits.

If the answer is yes: which platform?

We are not tied to a single vendor, which means the recommendation changes with the requirement rather than with what we have in stock.

If you would rather start from the service overview, see VoIP business telephone systems.

Five mistakes we see repeatedly

1. Specifying the phone system before the connectivity. Voice quality is decided by the line and the network, not the handset. Survey first.
2. Forgetting the non-voice lines. Lifts, alarms, door entry and card terminals must be identified before any line is ceased.
3. Buying per-user licences for people who don’t need them. A warehouse with one cordless handset does not need eight seats. Licence to the roles, not the payroll.
4. Ignoring the power-cut plan. A UPS and a failover rule take minutes to set up and are impossible to retrofit during the outage.
5. Leaving porting to the end. It is the longest lead-time item in the project and the only one that can delay go-live.

Frequently asked questions

Is VoIP right for a small business with only a few staff?

Usually yes, and often more clearly than for a large one. A small business gains the features it could never justify buying outright (auto attendant, voicemail to email, mobile apps on the business number) without on-site hardware. The saving is smaller in pounds, but the capability gain is larger.

Will my phones stop working if the internet goes down?

Handsets in the building will stop registering, yes. What matters is what is configured to happen next: calls to your main number can fail over automatically to mobiles or to the mobile app, so calls still get answered. With a UPS on the router and switch, and mobile data as a fallback, an outage becomes an inconvenience rather than a closed business.

Can I keep my existing phone number if I switch to VoIP?

Yes. Geographic numbers, including local 01604 numbers, can be ported to a VoIP platform. Allow several working days for the port and schedule it as a planned step rather than a same-day switch.

How much internet speed do I need for VoIP?

Around 100kbps per concurrent call in each direction, so ten simultaneous calls need roughly 1Mbps of upload. Stability matters more than headline speed: jitter and packet loss cause far more call-quality problems than bandwidth does. A full fibre connection removes the issue for almost all SMEs.

What happens to my alarm, lift line or card machine when the analogue lines go?

Each needs its own replacement plan: IP or mobile signalling for alarms and lift autodiallers, an analogue adaptor for simpler devices, or a broadband/IP-connected card terminal. Identify them during the site survey; they are the most commonly missed part of a migration.

Is VoIP secure enough for confidential business calls?

Yes, when it is set up properly. Business-grade platforms encrypt call signalling and media using TLS and SRTP, and handsets are provisioned securely. The realistic risks are weak passwords, unrestricted international dialling and unpatched routers. All are addressed at install with call barring, strong credentials and a properly configured firewall.

Do I need new handsets, or can I keep my existing phones?

Some existing IP handsets can be re-provisioned onto a new platform; analogue and older digital phones generally cannot, though an analogue adaptor can keep specific devices alive. It is worth checking the model before assuming either way; we do this as part of the survey.

Should I move now or wait until closer to the switch off?

Move ahead of it. Closer to the deadline, installer availability and porting slots become the constraint, and a forced migration is done to a network timetable rather than yours. Moving early also means the change is planned around your quiet period instead of someone else’s.

Can VoIP work with Microsoft Teams?

Yes. Teams can be given real external calling so staff dial and receive business calls in the app they already use, either through Operator Connect or by integrating a VoIP platform with Teams. It suits businesses already running their day inside Teams.

Next step

If you want a straight answer for your own business rather than a general one, the fastest route is a short conversation covering four things: your current lines and system, your broadband, what else is plugged into those lines, and how your calls actually come in. We will tell you honestly whether to move now, move on SIP first, or fix the connectivity before touching the phones.

See how we have done it for other UK businesses in our case studies, or speak to our team on 01604 812813.

Barton Telecom Services, Earls Barton, Northamptonshire. Installing and supporting UK business telephone systems since 1995. Over 100 five-star Google reviews. Last reviewed: 24 September 2026.