Business VoIP and Hosted Telephony for UK Businesses

What Is Business VoIP and Why Does Every UK Business Now Need It?

Voice over Internet Protocol (VoIP) is the technology that carries phone calls over broadband instead of traditional copper telephone lines. In 2025, BT completed its Public Switched Telephone Network (PSTN) switch-off — meaning the old analogue telephone infrastructure that UK businesses have relied on for decades is now officially retired. Any business still operating on legacy ISDN or PSTN lines will have been migrated already, but many have been moved to interim digital voice products that do not take advantage of full hosted VoIP capabilities.

This guide explains what hosted VoIP is, how it compares to traditional phone systems, what features to expect, and how to choose the right system for a UK SME.

The BT PSTN Switch-Off: What It Means for Your Business

The PSTN (Public Switched Telephone Network) and its digital successor ISDN were the backbone of UK business telephony for decades. BT's switch-off programme, completed in 2025, has retired this infrastructure entirely. If your business had ISDN lines, BT or your incumbent provider will have migrated those lines to either Digital Voice (a basic VoIP product) or will have ceased them entirely.

Basic Digital Voice products from BT and other carriers are not the same as a full hosted VoIP or cloud PBX system. Digital Voice maintains basic inbound and outbound calling, but does not include the advanced features — auto-attendant, call recording, multi-site extension dialling, CRM integration — that a proper business VoIP platform delivers.

The switch-off is an opportunity to upgrade your telephony properly, rather than simply continuing with a like-for-like migration from one legacy system to another.

VoIP vs Traditional Landlines: Cost and Feature Comparison

The most immediate benefit of VoIP for most UK businesses is cost. Traditional ISDN lines cost £25–£50 per channel per month in line rental alone, before call charges. A hosted VoIP system typically costs £5–£15 per user per month with inclusive UK calls.

• Line rental: ISDN — £25–£50 per channel. VoIP — typically zero; calls are included in the monthly per-user fee.
• International calls: Traditional systems charge per minute at retail rates. VoIP typically offers inclusive minutes or materially lower per-minute rates.
• Features: Call recording, auto-attendant, IVR, and call queuing are standard on hosted VoIP. On legacy ISDN, each feature required additional hardware or a separate contract.
• Scalability: Adding a new extension on a legacy PBX required a physical line and hardware changes. On hosted VoIP, new users are provisioned in minutes through a web portal.
• Remote working: VoIP extensions work on any device with an internet connection — laptop, mobile phone, or desk phone — making remote and hybrid working seamless.

Microsoft Teams Calling: Is It the Same as VoIP?

Microsoft Teams includes chat, video, and file sharing as standard in Microsoft 365. However, basic Teams does not include PSTN calling — the ability to make and receive calls to external phone numbers. There are two main ways to add calling to Teams:

Microsoft Teams Direct Routing

Direct Routing connects your Teams environment to a telephony provider's SIP trunk, giving your users the ability to make and receive calls to any UK or international number directly from Teams. This is managed by AMVIA and uses your existing Microsoft 365 licences (Business Basic, Standard, or Premium).

Microsoft Calling Plans

Microsoft also sells its own Calling Plans as an add-on to Teams. These are simpler to set up but typically more expensive per user and offer less flexibility than Direct Routing, particularly for businesses with complex call routing requirements or multiple UK numbers.

For most UK SMEs already on Microsoft 365, Teams Direct Routing through AMVIA delivers the best value — combining your existing Microsoft investment with PSTN calling capability and a full cloud PBX feature set.

Hosted VoIP vs On-Premise PBX

Some larger businesses still operate on-premise PBX hardware — physical telephone exchange equipment installed on-site. While this gave full control historically, on-premise PBX systems are reaching end-of-life and require significant capital expenditure to maintain or replace.

Hosted VoIP (cloud PBX) eliminates the on-premise hardware entirely. The PBX functionality runs in a data centre managed by the provider, and your business accesses it over the internet. This reduces upfront capital expenditure to near zero, removes the need for on-site maintenance, and makes the system accessible from anywhere.

What Internet Speed Do You Need for VoIP?

Each concurrent VoIP call typically requires around 100 kbps of upload and download bandwidth. For most UK businesses on standard business broadband, this is not a constraint for small teams. However, if your business makes a large number of concurrent calls, or if your internet connection is heavily contended (shared with many other users), call quality can degrade.

For businesses with 20+ concurrent calls, or for those requiring guaranteed call quality, a leased line provides the uncontended, symmetric bandwidth that VoIP demands. AMVIA provides both VoIP and leased line services, and will assess your bandwidth requirements as part of any VoIP proposal.

How to Choose a Business VoIP Provider

• Number porting: Any reputable VoIP provider should be able to port your existing business numbers to their platform. Confirm this before signing.
• Failover options: What happens if your internet connection goes down? Good VoIP systems support failover routing to mobile numbers or alternative sites.
• Call recording and compliance: If your business is regulated (financial services, legal, healthcare), confirm the provider's call recording solution is compliant with your sector's requirements.
• Microsoft Teams integration: If your team uses Teams, a provider that supports Direct Routing will deliver a more unified experience than a standalone VoIP system.
• UK-based support: When telephony fails, you need fast support. Ensure your provider offers UK-based engineering support with a defined SLA.

Business VoIP for Different Business Sizes

Small businesses (5–25 staff): A simple hosted VoIP system with auto-attendant, voicemail-to-email, and mobile app calling covers most requirements. Microsoft Teams Direct Routing is often the most cost-effective solution if you are already on Microsoft 365.

Mid-market businesses (25–100 staff): Multi-site call routing, call recording for compliance, CRM integration, and call queuing become important at this scale. A dedicated cloud PBX platform with a management portal gives administrators full control.

Larger SMEs (100–500 staff): High call volumes require careful capacity planning, advanced IVR, call centre features, and integration with CRM systems. AMVIA designs and manages bespoke VoIP architectures at this scale.