Before the Dial Tone Dies: A Small Firm's Line-by-Line Plan for the PSTN Retirement

The phrase 'PSTN switch-off' sounds like something for telecoms engineers and large estates. In practice, it lands on small businesses as a surprisingly ordinary question: what exactly is plugged into that phone socket, and what happens when the old network is no longer there?

In 2026, that question has moved from the back of the drawer to the front of the to-do list. Openreach plans to retire the public switched telephone network at the end of January 2027, and the stop-sell of traditional analogue lines has already reached most of the country. The sky is not falling. But the deadline is real, and the businesses that glide through it are the ones that started with a clipboard rather than a panic.

What is actually changing

The PSTN is the old copper telephone network that has carried analogue voice calls for decades. It also carries a surprising number of things that are not, strictly speaking, phones. When it goes, a standard phone socket will not keep working simply because you are still paying for a line.

Most replacements are VoIP services, which run over your broadband rather than a separate telephone line. That is usually good news: clearer calls, easier numbering, lower bills, voicemail that arrives by email. But VoIP assumes two things that analogue lines did not: working internet and working power. It also assumes that every device attached to the old line can either move to the new service or be replaced.

That last assumption is where small firms get caught out.

Start with the bill, not the box

Before anyone talks about handsets or tariffs, build a line inventory. Not a technical diagram — a spreadsheet with one row per line or number you pay for. For each one, capture:

• the telephone number and the line reference on the bill;
• what the line is used for, in plain English;
• the device or devices attached to it;
• who owns that device, including any maintenance contract;
• the contract end date and any early termination charge;
• who inside the business would notice if it stopped working.

This sounds dull because it is dull. It is also the single most useful hour you will spend on the project. Most small firms discover at least one line they had forgotten about, and at least one device they assumed was something else.

The devices people forget

The desk phone is the easy part. The awkward ones tend to be:

• intruder alarms and monitored alarm signalling, especially older systems that use a phone line to call the monitoring centre;
• lift and emergency help phones in buildings with passenger lifts;
• card payment terminals and EPOS systems that still dial out over a phone line;
• fax machines, usually kept for one supplier or one NHS department;
• door entry systems and gate intercoms;
• legacy modems for heating, CCTV, till systems or building management;
• out-of-hours answerphones and red care-style lines.

Some of these can move to VoIP with the right adapter or SIM. Some cannot, and need replacing. The point is not to guess. The point is to identify them early enough that replacing an alarm communicator is a planned cost, not an emergency.

Questions to ask before you port

When you speak to a provider, ask these questions in writing and keep the answers:

1. Does the number port include every service on the line, or only voice calls?
2. What happens to my alarm, lift phone or card terminal during and after the move?
3. What happens to calls if the broadband goes down?
4. What happens if the power goes off?
5. Who configures the router, the handsets and the call routing — us or you?
6. Can we keep our existing numbers, including any non-geographic ones?
7. How do we call 999 and 112, and what location information is passed to the emergency services?
8. What is the notice period, and what happens if the port date slips?

A good provider will answer these without sighing. If they cannot explain the alarm question, that is useful information.

Test the things you cannot see

A phone that rings is not proof that the move has worked. Before you cancel the old line, run a short test list:

• call in and out from each handset;
• test voicemail, hunt groups and any recorded messages;
• trigger the alarm and confirm the monitoring centre receives it;
• test the lift phone or emergency help point with the maintaining company;
• run a card payment and a refund on the EPOS or PDQ;
• send and receive a fax if you still rely on one;
• check caller ID and any numbers displayed to customers;
• make a test 999 call only with the provider's guidance, never as a prank.

Where possible, run the old and new systems in parallel for a week. It is far easier to fix a misrouted number when the old line is still live.

Do not forget power and broadband

VoIP is only as reliable as the connection underneath it. A consumer router and a domestic broadband service may be fine for a home office, but a small firm taking payments and handling bookings should think about a business-grade connection, a UPS for the router and key handsets, and a 4G or 5G backup for the broadband. That is not over-engineering; it is the equivalent of keeping a torch in the cupboard.

A simple sequence that works

1. List every line and number on the bill.
2. Label every device attached to those lines.
3. Ask the provider the awkward questions in writing.
4. Order the replacement service with a realistic lead time.
5. Run a parallel test, including alarms and payments.
6. Only then cancel the old line.

The PSTN retirement is not a reason to panic. It is a reason to open the stationery cupboard, find the clipboard and spend an afternoon being pleasantly boring about details. The firms that do that will barely notice the dial tone disappear.