How to switch your business from a landline to VoIP: a step-by-step guide

Moving from landlines to VoIP is not a like-for-like handset swap. It changes how calls reach you, what your network has to carry and what happens when something fails. Done in the right order it is straightforward, and with the UK PSTN switch-off rescheduled to January 2027 it is now a question of when, not whether. This guide walks through the process as we run it for businesses across Hertfordshire, west Essex and London.

Is your business ready to switch?

The clearest signals that a business is ready, or overdue, for VoIP:

• Staff work from home, from client sites or across more than one office and calls do not follow them.
• The phone bill keeps rising, particularly line rental and call charges across several sites.
• You want call recording, an auto-attendant, call queues, voicemail-to-email or CRM integration and the current system cannot provide them.
• The existing PBX is out of support, parts are hard to find or the maintainer has warned you about it.
• You have no visibility of missed calls, wait times or busy periods.
• Your lines are analogue or ISDN, which means they will stop working when the network is withdrawn.

If two or more of those apply, the rest of this guide is for you. If you are still weighing up the options, start with PSTN vs VoIP.

Step 1: audit what you have today

Phone systems grow organically. Numbers are added, routing rules change, and workarounds become normal. Before you change anything, write down:

• Every phone number you own, including DDIs, fax numbers, non-geographic numbers and any that are published but rarely used.
• Extensions, hunt groups, ring groups, call queues and the rules behind them (office hours, out-of-hours, holiday messages).
• Voicemail boxes and who monitors them.
• Contract end dates and notice periods for existing lines and maintenance.
• Anything else plugged into a phone line: alarm panels, lift emergency phones, card terminals, door entry systems, fax machines, franking machines, telecare devices.

That last point is the one businesses most often miss. Those devices will not work on a VoIP handset and each needs its own migration path. Our PSTN switch-off guide covers them one by one.

Step 2: test your connectivity and network

VoIP turns voice into data, so your broadband and internal network now carry your calls. Test them properly rather than assuming a connection that copes with email will cope with 15 concurrent calls.

Connectivity. Each call needs around 100 kbps each way, so bandwidth is rarely the problem. Latency (delay), jitter (variation in delay) and packet loss are. As rules of thumb, calls stay clear when latency is under about 150 ms, jitter under about 30 ms and packet loss under 1 percent. Test at the busiest time of day, not first thing. If the office is on a consumer-grade or heavily contended connection, budget for a business fibre service (FTTP or SoGEA) with a 4G or 5G backup.

Internal network. Older switches, unmanaged routers and long, poorly terminated cable runs cause more VoIP complaints than the VoIP platform ever does. Check that the router and switches support quality of service (QoS) so voice traffic is prioritised over backups, cloud sync and video meetings. Put desk phones on a separate voice VLAN where possible. If phones will be powered over Ethernet, confirm the switches supply enough PoE. Our structured cabling and office Wi-Fi work is often the precursor to a clean VoIP rollout.

Power. Analogue phones drew power from the exchange. VoIP phones need the router, switch and broadband equipment to stay up. A small UPS on the comms cabinet keeps calls running through a short power cut.

Step 3: choose the platform and the hardware

Hosted (cloud) VoIP is the right choice for almost every business of up to 250 people: no on-site phone server, per-user subscription, changes made through a web portal. Dig IT's VoIP and business phone systems service is built on 8x8, which combines calling, mobile and desktop apps, Microsoft Teams integration, call recording, queues and analytics on one platform.

When comparing platforms, look beyond the per-user price at:

• Call bundles and what is excluded (international, 084/087/09 numbers).
• Integration with Microsoft 365, Teams and your CRM or case management system.
• Reporting on missed calls, wait times and agent activity.
• Mobile app quality, because that is what field staff will actually use.
• Security: encrypted calls, strong authentication, fraud monitoring.
• UK support availability and who you actually ring when something breaks.

Hardware decisions affect adoption. Reception and anyone on the phone all day want a desk phone. Mobile and hybrid staff generally prefer an app and a good headset. Most businesses end up with a mix. Our article on what VoIP costs in the UK sets out the observed price ranges for licences, handsets and porting.

Step 4: plan the number port

Keeping your numbers is usually non-negotiable, and porting is the step with the longest lead time.

1. The new provider submits a port request with proof you own the numbers (a recent bill is usually enough).
2. The losing provider validates the request. Rejections are common when the account name, postcode or number list does not match their records exactly, so check the bill first.
3. A port date is agreed. Straightforward single-line ports often complete within a couple of weeks. Multi-line ISDN and DDI ranges can take longer.
4. On the port date, calls start arriving on the VoIP platform. The old lines then cease.

Two rules. Keep the old lines active until the port has completed, because cancelling first can lose the number. And build the new call routing on the VoIP platform before the port date, using temporary numbers to test it, so the switch is invisible to callers.

Step 5: build and test before go-live

Run the new system alongside the old for at least a week or two. During that time, test:

• Call quality on internal calls, external calls, mobile app calls, and calls made while a large backup or video meeting is running.
• Call flows: auto-attendant options, ring groups, queues, out-of-hours routing, holiday messages, voicemail-to-email.
• Failover: pull the broadband and confirm calls divert to mobiles or the backup connection as designed.
• Integrations: caller records appearing in the CRM, click-to-dial, call logging.
• Devices: every desk phone registered, every app logged in, headsets working.
• Emergency calls: confirm the registered address for 999 calls is correct for each site.
• Security: strong passwords or single sign-on, admin access limited, international dialling restricted where it is not needed.

Fix what you find, then set the cut-over date.

Step 6: cut over, train and monitor

Brief staff a few days ahead with a one-page guide: how to transfer, how to pick up a queue call, how to set presence, how to use the mobile app. Keep the training short and practical. Most resistance to a new phone system comes from people who were never shown the three things they do every day, not from the technology itself. Have an engineer available on the morning of cut-over so small problems are fixed in minutes rather than logged as tickets.

In the first month, review the analytics for missed calls and long waits, tune the routing, and remove any old lines that are still being billed. Check the first invoice against the quote, because unused numbers and forgotten lines have a habit of surviving the migration.

A typical timeline for a single-site firm of 20 to 40 people:

Broadband upgrades and complex ports push this out, which is why starting well ahead of the 31 January 2027 switch-off matters.

Common mistakes to avoid

• Cancelling the old lines before the port completes.
• Forgetting the alarm, the lift line or the card terminal until the day they stop working.
• Assuming the existing router will prioritise voice without configuration.
• Putting desk phones on Wi-Fi.
• Buying the cheapest per-user plan and then paying for every call to a mobile.
• Leaving the platform with default passwords and unrestricted international dialling, which is how toll fraud happens.
• Treating go-live as the end. Reports and routing need a review after the first month.

What to do next

If you would like the switch handled as one project, from audit through porting to the first month's review, Dig IT covers connectivity, network, 8x8 deployment and ongoing support as one accountable team. Talk to an engineer about your current lines and we will map out the timeline for your business.