Most comparisons of VoIP and traditional landlines focus on headline monthly costs. That comparison misses most of what actually determines the real cost difference. Line rental, call charges, hardware depreciation, maintenance, multi-site connectivity, and the cost of features that are standard on VoIP but charged as add-ons on traditional systems — all of these matter.
This guide is a true cost comparison. We will give you real numbers for a typical UK small business in 2026, show you exactly where VoIP saves money and where it does not, and help you make a properly informed decision.
The short answer:
- For most UK businesses with 3–50 users, VoIP costs 40–65% less than an equivalent traditional phone system
- The savings come primarily from: no line rental per user, included call bundles, free internal calls, and no per-feature charges
- Hardware costs are comparable; VoIP handsets cost similar amounts to ISDN handsets
- The PSTN switch-off means traditional landlines are not a long-term option regardless of cost
- The break-even on switching to VoIP from a traditional system is typically under 6 months
What a traditional landline actually costs
Many business owners underestimate their traditional phone bill because it is split across multiple invoices and never examined closely.
A traditional UK business phone system has these cost components:
Line rental
BT Business line rental for a standard analogue business line runs £18–£22 per month per line. An ISDN2e (2-channel digital line) runs £30–£45 per month. An ISDN30 (30-channel) runs from £120/month upward.
A business with 5 staff needing 5 simultaneous calls needs, at minimum, an ISDN2e pair plus an additional ISDN2e, or a small ISDN30 — roughly £60–£90/month in line rental alone, before a single call is made.
Call charges
Traditional business calls are charged per minute. UK local and national calls on BT Business run 1.5p–3p per minute during business hours. Premium numbers (0844, 0871) and international calls are significantly higher. A business making 1,000 minutes of calls per month pays £15–£30 in call charges.
PBX hardware and maintenance
A traditional ISDN phone system requires an on-premises PBX — a hardware box that manages extensions, routing, and voicemail. Entry-level PBX hardware for a small business costs £500–£2,000. Maintenance contracts run £200–£800/year. PBX hardware depreciates and typically requires replacement every 7–10 years.
Per-feature charges
Features like call recording, auto-attendant (IVR), and call queuing are add-ons on traditional systems. A call recording solution for a small business PBX can cost £500–£2,000 in hardware plus ongoing software fees.
Total: traditional landline for a 5-user business
| Component | Monthly cost |
|---|---|
| Line rental (ISDN2e × 2) | £70 |
| Call charges (1,000 min/month) | £20 |
| PBX maintenance (amortised) | £40 |
| Feature add-ons | £25 |
| Total | £155/month |
What VoIP actually costs
VoIP has a fundamentally different cost structure. There is no physical line rental — calls travel over your existing internet connection. The system is hosted, so there is no on-premises PBX to buy or maintain. Features that are expensive add-ons on traditional systems are standard on VoIP.
Using VoIPNinjas as the example:
| Plan | Per user/month | 5 users total |
|---|---|---|
| Ronin | £5.99 | £29.95 |
| Samurai | £14.99 | £74.95 |
| Shogun | £24.99 | £124.95 |
The Samurai plan includes 750 minutes per user per month (3,750 minutes for 5 users), call recording, voicemail to email, auto-attendant, mobile app, and unlimited internal calls. There is no line rental. There is no PBX to maintain. Features are included.
Total: VoIP for a 5-user business (Samurai plan)
| Component | Monthly cost |
|---|---|
| VoIPNinjas Samurai × 5 | £74.95 |
| Broadband (existing) | £0 (already paying) |
| Hardware maintenance | £0 (hosted) |
| Feature add-ons | £0 (included) |
| Total | £74.95/month |
Saving vs traditional: £80.05/month — £960/year
Where the real differences are
Internal calls
On a traditional ISDN system, internal calls between extensions are free only if they are on the same PBX. A second office on a separate PBX incurs call charges.
On VoIP, all internal calls between extensions on the same account are free, regardless of location. A Bournemouth office and a London sales rep calling each other costs nothing. This is a significant saving for businesses with multiple sites or remote staff.
Scalability costs
Adding a user on a traditional ISDN system may require adding a new ISDN channel (£30–£45/month more in line rental) and a new handset licence on the PBX.
On VoIP, adding a user is adding a plan — £5.99 to £24.99/month, depending on the plan, with nothing else. Scale up or down on 28 days’ notice.
International calls
Traditional international call rates via BT Business are expensive: 5p–15p/minute for Europe, higher for further destinations.
VoIPNinjas Shogun includes calls to 55 countries in the monthly fee. For businesses with regular international call needs, this alone can represent £50–£200/month in savings.
Feature costs
Call recording: £0 extra on VoIPNinjas vs £500–£2,000 setup on traditional PBX.
Auto-attendant (IVR): £0 extra on VoIPNinjas vs £200–£500 on traditional.
Voicemail to email: £0 extra on VoIPNinjas vs add-on cost.
Where VoIP does NOT save money
Broadband
VoIP requires a decent internet connection. If you are on a slow or unreliable connection, you may need to upgrade — typically £10–£30/month more for a better business broadband package. Factor this in. On the other hand, a broadband upgrade is a benefit in its own right, not a pure VoIP cost.
Handsets
VoIP handsets cost similar amounts to traditional ISDN handsets. A Yealink T31P is £50–£65; a comparable ISDN desk phone is similar. If you are buying new handsets at migration time, this is not a VoIP-specific cost. If you already have compatible handsets (many post-2015 Yealink, Snom, Polycom handsets are compatible), there may be no hardware cost at all.
Alarm and card terminal lines
If your business uses a dedicated analogue line for an intruder alarm, fire alarm, or card terminal, that line needs separate attention. Some alarm systems work over VoIP with adapter hardware; others need a GSM backup unit. This is an additional cost that varies by installation.
The migration cost
Switching from ISDN to VoIP has a one-time cost: number porting (typically included by good providers), any new handsets needed, and the time to configure the new system.
VoIPNinjas charges no setup fee and includes number porting in the plan. The main cost is your time and any new handsets. For most businesses, the monthly savings from VoIP cover the cost of new handsets within two to three months.
Five-year total cost comparison: 5-user business
| Traditional (ISDN) | VoIP (Samurai) | |
|---|---|---|
| Monthly recurring | £155 | £74.95 |
| 5-year recurring | £9,300 | £4,497 |
| PBX hardware (amortised) | £800 | £0 |
| Feature setup costs | £1,000 | £0 |
| 5-year total | £11,100 | £4,497 |
| Saving | £6,603 |
These figures use conservative estimates. Real traditional ISDN costs are often higher once maintenance, channel expansion, and feature upgrades are included.
The PSTN switch-off removes the question
For many businesses, the cost comparison is academic: traditional ISDN is being switched off. There is no option to stay on it past January 2027. The question is not whether to switch to VoIP — it is which VoIP system to choose and when to migrate.
Migrating now rather than under deadline pressure means you choose on your terms, you test thoroughly before go-live, and you start saving money immediately.
See the savings for your business
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