VoIP for Business UK: The Complete Guide (2025)

If your business still relies on a traditional phone line, you have less than two years to act. Openreach is switching off the UK's entire PSTN and ISDN network in January 2027, and the businesses that migrate now pay less every month in the meantime — not as a reward for acting early, but because VoIP simply costs less than ISDN. This guide covers everything you need to know about VoIP for business in the UK: what it is, what it costs, which features matter, and how to switch without disruption.

The short answer:

• VoIP (Voice over Internet Protocol) routes calls over your internet connection instead of copper phone lines
• UK businesses switching from ISDN to VoIP typically reduce telecoms costs by 50–75%
• 31% of UK businesses have already made the switch; the PSTN deadline means the rest must follow by January 2027
• Setup takes 10 working days; there are no long contracts with the right provider
• The free 14-day trial from VoIPninjas means you can verify call quality on your own connection before committing

What is VoIP for business?

VoIP — Voice over Internet Protocol — converts your voice into digital data and transmits it over the internet, rather than through the copper telephone network. For your team, the experience is identical to a traditional phone call: you dial a number, someone picks up, you talk. The difference is entirely in the plumbing.

For businesses, VoIP comes in two primary forms:

Hosted VoIP (cloud phone system) Your phone system runs in the cloud, managed by your provider. Calls travel over your broadband or leased line. You access the system via IP handsets on desks, a softphone app on a laptop, or a mobile app on a smartphone. There is no on-site server, no PBX hardware to maintain, and features like call recording, voicemail-to-email, and ring groups are managed through a web dashboard.

SIP trunking If your business already has an on-site PBX, SIP trunking replaces the ISDN circuits feeding it with internet-based lines, while keeping the existing phone system in place. Each SIP trunk supports one simultaneous call. This approach suits businesses with a recent, SIP-compatible PBX they want to retain.

For most UK SMEs, hosted VoIP is the cleaner choice — it replaces an ageing ISDN setup with a modern, cloud-based system rather than extending the life of infrastructure that is approaching its end anyway.

Why VoIP costs less than what you are paying now

The numbers are straightforward. ISDN channels typically cost £30–£50 per channel per month in line rental alone, before call charges. For a 10-person office with an ISDN2e connection (2 channels) and an ISDN30 line (10 channels), that is £360–£600 per month in line rental.

A comparable VoIP setup for 10 users:

The Samurai plan at £149.90/month for 10 users includes 750 minutes per user per month, call recording, voicemail-to-email, ring groups, mobile app, and auto-attendant. No equivalent ISDN setup comes close to that feature set at that price point.

UK businesses switching from ISDN to VoIP typically save 50–75% on their telecoms costs, according to research across the UK SME market. For most businesses, the saving is immediate — starting from the first month after migration.

VoIP features that matter for UK SMEs

The features that make VoIP genuinely useful for a small business are not the ones that vendors tend to lead with. Here is what actually changes day-to-day operations:

Voicemail to email Missed calls leave a voicemail, which is transcribed and emailed to the recipient as an audio file and text. No more dialling in to check messages — they appear in your inbox with the caller's number and a timestamp.

Ring groups and hunt lists Incoming calls ring multiple team members simultaneously or in sequence until someone answers. For a small team without a dedicated receptionist, this removes the risk of calls going unanswered.

Call forwarding and mobile integration Your office number rings your mobile when you are not at your desk. For business owners and managers who are frequently out of the office, this means never missing a call on a number customers already know.

Call recording Calls are recorded automatically and stored in your account dashboard. For businesses in regulated sectors, client services, or training environments, this is an essential feature — and it is included as standard, not an expensive add-on.

Auto-attendant (IVR) A professional recorded greeting routes callers to the right department or team member without needing a receptionist to handle every call. "Press 1 for sales, press 2 for support" — configurable in minutes through your web dashboard.

Number flexibility Add or remove user licences instantly. Add new geographic numbers (01/02) for different locations. Set up 0800 numbers. Route calls differently for bank holidays, out of hours, or staff absence. All of this is configuration, not engineering.

What you need to run VoIP

A stable internet connection Each active VoIP call uses approximately 100Kbps of bandwidth. A team of 10 with 5 simultaneous calls needs 500Kbps of consistent bandwidth dedicated to voice. A standard FTTC or FTTP broadband connection handles this comfortably. ADSL can work but is being switched off with the PSTN in January 2027 — upgrade now.

The right router and network setup Your router needs to support Quality of Service (QoS) settings to prioritise voice traffic over other internet traffic. Most business-grade routers do this. Your VoIP provider should check your setup during onboarding.

Handsets, headsets, or a softphone app IP handsets (£40–£150 each) are the closest equivalent to a traditional office phone. Softphones — apps for your laptop or desktop — cost nothing and work on any device. Mobile apps mean your team can use their business number from anywhere. Most businesses use a mix.

Choosing a VoIP provider: what to look for

Not all VoIP providers are structured the same way. The most important question to ask is: are you a direct provider, or a reseller?

Resellers buy wholesale VoIP services from a carrier and add a margin. They have less control over the underlying network, less ability to diagnose and fix problems, and another layer between you and the infrastructure when something goes wrong.

A direct provider — like VoIPninjas — owns the infrastructure. When you call support, the person answering can actually make changes to the network. When there is a fault, there is no escalation queue to a third-party carrier.

Beyond that, look for:

• No long contracts. You should not need to sign 24 months to migrate before a forced deadline. A 28-day rolling agreement is the standard you should expect.
• A free trial. Call quality depends partly on your internet connection. A good provider lets you test it on your own setup before committing.
• Transparent pricing. The monthly per-user cost should be the complete cost. Ask specifically about setup fees, number porting fees, and exit penalties.
• UK support you can actually reach. Response times and support quality vary significantly between providers. A local UK support team matters more when something goes wrong mid-business-day.

The 2027 PSTN switch-off: why waiting costs you money

Every month you stay on ISDN, you are paying £30–£50 per channel for a product that is being withdrawn in January 2027. The forced migration is coming regardless — the only variable is whether you control the timing.

Businesses migrating now:

• Pay less immediately (VoIP is cheaper than ISDN from day one)
• Migrate on their own schedule, with time to test and configure
• Avoid the backlog of last-minute migrations in late 2026
• Have access to provider support capacity that will be stretched as the deadline approaches

The earlier you act, the more of the cost saving you capture. A business migrating in January 2025 saves approximately two years of the monthly difference between ISDN and VoIP costs before the mandatory deadline. For a 15-person team, that saving runs to several thousand pounds.

How VoIPninjas compares

VoIPninjas is a direct UK provider — not a reseller — based in Christchurch on the South Coast. We own our infrastructure, which means our support team has direct access to fix problems rather than logging tickets with a wholesale carrier.

Our plans start at £5.99/user/month (Ronin) on a 28-day rolling agreement — no long contract, no setup fee, no exit penalty. The Shogun plan at £24.99/user/month includes unlimited calls to UK landlines, mobiles, and 55 countries — the right choice for high-volume teams or businesses with regular international calls.

What makes the difference in practice:

• Free 14-day trial — no card required, every feature enabled, running on your actual connection
• Number porting included — your existing numbers transfer at no extra cost
• Most businesses are fully live within 10 working days
• Local UK support from our Christchurch team — not a call centre in another time zone

We serve businesses across Dorset, Hampshire, and the Channel Islands, as well as nationally. If you have a complex ISDN setup — multiple circuits, alarm systems, PDQ terminals — talk to us before you do anything. We will audit the full picture before recommending a migration plan.

Start your free VoIP trial today No tie-in, no setup fees. Most businesses are fully live within 10 working days. Get a Free Quote — or call us: 0330 043 2388

Frequently asked questions

Is VoIP reliable enough for a business phone system?

On a stable FTTC, FTTP, or leased line connection, modern hosted VoIP equals or exceeds the reliability of ISDN. The key variable is your internet connection quality — consistency matters more than headline speed. A stable 30Mbps connection handles VoIP better than an unstable 100Mbps. Your provider should test your connection during onboarding. VoIPninjas' free 14-day trial gives you real call quality data on your own connection before you commit.

Can I keep my existing phone numbers when switching to VoIP?

Yes. Number porting transfers your existing 01, 02, and 03 numbers to the new VoIP system. The process takes 5–10 working days. Your current lines stay active until porting completes — there is no gap where your numbers are unreachable. VoIPninjas handles the porting request on your behalf.

Do I need new phones to switch to VoIP?

Not necessarily. You can use IP handsets (desk phones built for VoIP), softphone apps on laptops, or mobile apps on smartphones. Analogue telephone adaptors (ATAs) can connect existing analogue handsets to a VoIP system. Most businesses use a combination — mobile apps for staff who move around and IP handsets for reception or main office desks.

What internet speed do I need for VoIP?

Each active VoIP call uses approximately 100Kbps. A team of 10 with 5 simultaneous calls needs 500Kbps dedicated to voice — a fraction of any standard broadband connection. The bigger requirement is stability. Jitter and packet loss degrade call quality more than low raw speed. Your VoIP provider should assess your connection quality during onboarding.

How long does it take to switch to VoIP?

With VoIPninjas, most businesses are fully live within 10 working days of confirming their order. The main variable is number porting, which takes 5–10 working days and runs in parallel with the rest of the setup. We recommend starting at least 3 weeks before your target go-live date to allow for porting, configuration, and testing.