VoIP vs Traditional Landline for Business: Full Comparison 2026

With the PSTN switch-off deadline of 31 January 2027 approaching, every UK business needs to understand what is changing, what their options are, and why acting now — rather than waiting — is the right decision. This guide explains the difference between traditional landlines and VoIP, your migration routes, and how to choose the right solution for your business.

What is being switched off?

The PSTN switch-off affects every type of traditional copper telephone line in the UK:

• Analogue phone lines (PSTN/POTS) — standard single business landlines used for voice calls, fax, alarms and card terminals
• ISDN2 — digital lines typically providing 2 channels, used by smaller businesses with basic PBX systems
• ISDN30 — higher capacity digital circuits providing up to 30 channels, used by larger businesses with on-premise PBX phone systems

All three are on stop-sell from BT — no new connections can be ordered anywhere in the UK. All existing connections will be permanently terminated on 31 January 2027.

What is VoIP?

VoIP (Voice over Internet Protocol) carries telephone calls over your broadband connection instead of copper telephone lines. From the user's perspective it works identically to a traditional phone — you dial a number, it rings, you have a conversation. The difference is entirely in how the call travels.

VoIP offers significant advantages over traditional landlines: lower cost, more features, greater flexibility, and it works on smartphones and computers as well as desk phones. Most businesses that switch find their monthly phone bill reduces substantially.

Option 1 — You have a single analogue line

This is the most common scenario for small businesses. You have one phone line, possibly with a handset or a small multi-handset setup all connected to that single line.

The solution is straightforward: an ATA (Analogue Telephone Adapter) or a broadband router with a built-in ATA port. This is a small device that connects to your broadband router and provides one or more standard analogue phone sockets — exactly the same type your existing phones plug into.

The key benefit: you can keep any analogue phone you already own. A single ATA or voice-ready router can support multiple handsets connected to the same line — so if you have a cordless phone system with a base station and several handsets around the office, they all continue to work exactly as before. Your customers call the same number, your phones ring the same way.

Option 2 — You have multiple lines or an ISDN connection

If your business has multiple phone lines, an ISDN2 or ISDN30 circuit, you almost certainly have an on-premise telephone system (PBX) connecting them. The right migration route depends on whether that system supports VoIP.

Is your existing phone system SIP-compliant?

The first question to ask is whether your current PBX supports SIP trunks — the VoIP equivalent of your ISDN lines. Many modern and relatively recent PBX systems do. If yours is SIP-compliant, you have two options:

• Replace ISDN lines with SIP trunks — your existing phone system stays in place, only the lines change. This is often the lowest-cost migration route. You may need additional licences or a firmware upgrade from your PBX manufacturer.
• ATA or SIP-to-ISDN gateway — we can supply adapters that connect between your existing ISDN PBX and a SIP trunk, allowing migration without any changes to the phone system itself.

Your phone system is not SIP-compliant

If your existing PBX doesn't support SIP trunks, or is too old to upgrade cost-effectively, you'll need to replace it. At this point you have a choice between two approaches:

Hosted VoIP (cloud-based)

The phone system lives in the cloud — managed by your provider, not on your premises. This is the most popular route for most businesses and has significant advantages:

• Resilience — if your office loses power or internet, calls can automatically divert to mobile numbers. The system itself never goes down.
• No hardware maintenance — software updates, security patches and capacity management are all handled by the provider
• Work from anywhere — staff can use their office number on a smartphone or laptop from any location
• Scale instantly — add or remove users in minutes without engineer visits
• Lower upfront cost — no capital expenditure on on-premise hardware
• Automatic upgrades — new features added without cost or disruption

On-premise VoIP (IP PBX)

A new IP-based phone system installed at your premises, connected to SIP trunks for external calls. This approach suits businesses with specific requirements:

• Complex or highly customised call routing that's difficult to replicate in a cloud system
• Regulatory requirements for on-site data processing
• Very large sites where an on-premise system is more cost-effective at scale
• Sites with poor or unreliable internet connectivity

For most UK SMEs, hosted VoIP delivers better resilience, lower cost, and greater flexibility than an on-premise replacement — and removes the ongoing burden of maintaining physical hardware.

Cost comparison

Switching to VoIP almost always reduces monthly telecoms costs. Traditional landline and ISDN products typically cost £20–40 per line per month in line rental alone, before call charges. VoIP replaces this with a single per-user monthly fee that includes generous call bundles:

• GoYap: from £8.95/user/month (24-month contract) — includes 2,500 landline + 2,500 mobile minutes
• Gamma Horizon: from £9.95/user/month — includes 2,000 landline + 2,000 mobile minutes
• Microsoft Teams Phone: from £6.60/user/month via Direct Routing
• eve — Enterprise UCaaS: from £9.75/user/month
• BT Cloud Voice: from £9.52/user/month (note: rises by £1/user every April)

Broadband requirements for VoIP

VoIP runs over your broadband connection, so a reliable internet line is essential. Each simultaneous call uses approximately 100Kbps of bandwidth — so a 10Mbps connection can support many calls at once. Raw speed is rarely the issue.

What matters more is stability — low latency, low jitter, and minimal packet loss. Full fibre FTTP broadband performs best for VoIP. If you're currently on an older FTTC product bundled with a phone line, that product will be discontinued anyway as part of the switch-off, so upgrading your broadband at the same time makes sense.

We check your broadband suitability as part of every migration — and can supply business broadband alongside your new phone system on a single monthly bill.

Can I keep my existing number?

Yes — in almost all cases. Number porting transfers your existing business phone number to your new VoIP system. Your customers experience no change. Porting typically takes 7–14 working days. As the January 2027 deadline approaches, porting queues are expected to lengthen — so the sooner you start, the smoother the process.

Frequently asked questions