VoIP Phone System for Business | The Essential Guide

The AMVIA Team 12 min read · Mar 2026

This is the guide we send business owners and IT decision-makers who want a straight answer on business VoIP — what it is, what it costs, who the credible providers are, and how to move without breaking anything. It covers every question we field when a UK SME evaluates the switch from old PSTN/ISDN lines to internet telephony.

What is a VoIP phone system?

VoIP (Voice over Internet Protocol) carries telephone calls as digital data over an internet connection rather than as analogue signals over copper wire. Your voice is converted to data packets, sent across the internet, and reassembled at the other end in real time, with no perceptible delay on a sound connection.

A business VoIP system — also called a hosted PBX or cloud phone system — layers full call-management functionality on top of that: extensions, call routing, voicemail and auto-attendant, delivered as a cloud service rather than a box in your comms cupboard. AMVIA deploys this as a fully managed hosted phone system, so there is no on-site PBX to maintain.

Why is VoIP replacing traditional phone systems?

Three forces are pushing UK businesses off legacy lines: the regulated retirement of the copper network, a clear cost gap, and a feature gap that old PBX hardware cannot close. The deadline is the part most businesses underestimate.

• PSTN switch-off: Openreach is retiring the analogue PSTN and ISDN network, after which every UK business must run telephony over IP. See the official Openreach PSTN switch-off programme and plan your PSTN switch-off migration early.
• Cost advantage: VoIP from £5.95/user/month is typically 40–60% cheaper than equivalent PSTN/ISDN costs.
• Feature advantage: Hosted VoIP bundles call analytics, CRM integration, mobile working and call recording — capabilities traditional PBX systems only add through expensive bolt-ons.

The UK regulator's own Ofcom guidance on moving to digital landlines confirms the migration affects every phone line in the country, not just office systems.

What features does a business VoIP system include?

Business VoIP tiers up by capability. Entry plans cover everyday call handling; mid-tier plans add recording, analytics and integrations most SMEs want; enterprise plans add contact-centre tooling. Map features to what your team actually does before you pay for a tier you will not use.

If your business runs on Microsoft 365, Microsoft Teams calling can become your phone system directly — keeping voice inside the tool your staff already live in.

How much does business VoIP cost in the UK?

Most UK SMEs start from £5.95 per user per month, depending on the feature tier. Hardware is the main one-off: IP desk phones run £80–£200, while softphone and mobile apps are normally included at no extra cost.

• Entry (from £5.95/user/month): Core calling, voicemail, basic routing — a simple cloud phone system.
• Mid (from £5.95/user/month): Full feature set including recording, analytics and CRM integration. Suits most UK SMEs.
• Enterprise (from £5.95/user/month): Contact centre, AI features and API access for customer-service operations.

Always price the full contract term, not the headline per-user figure — porting, hardware and support all factor into total cost of ownership.

What internet connectivity does VoIP need?

VoIP is light on bandwidth but strict on quality. Each call uses roughly 100 kbps in each direction, so ten concurrent calls need about 1 Mbps reserved for voice. Low latency (under 150 ms) and low jitter matter far more than raw download speed.

Business-grade FTTP is adequate for most SMEs. For business-critical voice, a dedicated leased line gives you guaranteed bandwidth and an SLA-backed connection, so call quality does not degrade when the office network gets busy. The underlying signalling usually runs on SIP trunks, which connect your phone system to the public network.

How do you choose a VoIP provider?

Judge providers on five things: feature fit against your actual requirements, full-term pricing, uptime SLA (99.99%), UK-based support quality and response time, and integration depth. Headline price alone is the most common — and most expensive — mistake.

Provider prices above are indicative market figures, not AMVIA quotes. For Teams Phone specifics, Microsoft's official Microsoft 365 plans page is the authoritative source.

How do you plan a VoIP migration?

A clean migration is sequenced, not rushed. The order is: telephony audit, connectivity assessment, provider configuration, number porting, hardware provisioning, secondary-line migration, then go-live testing. Number porting alone takes 5–10 working days (typical UK 2026 timescale), so it sets your timeline.

Most well-managed SME migrations complete within 2–3 weeks. The work that derails projects is almost always the unglamorous part — the lines nobody remembers until they stop working.

Common migration mistakes

• Overlooking secondary lines: alarms, lifts, payment terminals, door entry
• Porting numbers before the new system is tested and ready
• Not testing call quality on the live connection before porting
• Underestimating staff training time on softphone apps
• Choosing a provider on price alone without verifying feature coverage

Because voice now rides your network, treat VoIP security as part of the migration — encryption, locked-down admin access and firewall rules limiting SIP traffic to your provider, not an afterthought.