When businesses prepare for the end of traditional phone lines, the office handsets are usually the first thing they look at. The phones are what everyone uses and what a provider asks about first. The date they’re preparing for is 31 January 2027. Openreach says every traditional phone line moves to a digital service by then, and Ofcom confirms that BT plans to retire its old landline network, the public switched telephone network (PSTN), by the same date. Other networks, including Virgin Media O2 and KCOM, have their own plans, with no dates set yet. 

The handsets are the easy part of that work. The line itself is changing, from the wall socket to the broadband router, and anything wired to it years ago will feel the change without appearing on any project plan. Those forgotten connections, more than the phone system, decide how much time a business needs. 

Your phone line does more jobs than your phone system 

Openreach’s guidance for businesses lists the equipment that may be tied to a phone line, and it goes well beyond office telephones. It includes alarm systems, fire alarm monitoring, CCTV, payment card terminals, door entry systems and lift emergency phones. Each can depend on a line to do its job, from calling a monitoring centre to taking a card payment. 

Broadband can be one of those dependencies too. Services delivered over copper phone lines share infrastructure with traditional phone services, and Openreach tells businesses on copper broadband to look at their options now. What changes for your own connection depends on the service you have, so ask your provider to confirm it. 

Power is another dependency. A digital phone line works through the router, so it needs mains electricity along with broadband, and Openreach says business lines may not work in a power cut without backup power. Any alarm that relies on the line to raise the alert needs a plan for when the power is off. 

That equipment gets missed because no project covers it 

Replacing the office phones is a project with an owner and a budget. Alarms and card terminals tend to be installed by their own suppliers, often years apart from the phone system, and may not appear on any IT asset list. They keep working, so nothing prompts anyone to check them until the line they depend on changes. 

How an alarm or card terminal copes with a digital line depends on its age and how it connects. Openreach says some equipment needs upgrading or reconfiguring, and only the supplier can confirm which applies to yours. 

The audit has to come before anything else 

Openreach points out that businesses tend to have more equipment connected to their phone lines than households do, which makes the switch a longer job. It lists longer lead times for equipment upgrades and compatibility testing among the risks of leaving it late. A provider can only plan a migration around the equipment it knows about, so every supplier left uncontacted holds up the clock on lead time. Openreach also expects demand to rise as January 2027 approaches, which gives earlier requests more choice of installation slots. 

The stakes are practical. A business still on a traditional line after 31 January 2027 may be moved to a temporary emergency voice-only service, which may not support the calling features it uses today, or it may lose service altogether. The ISDN switch-off follows the same date, and Openreach says services supported by ISDN must move to an IP service by then or it will be switched off. 

The audit itself is short, and whoever looks after your premises or IT can run it. 

1. Find out which traditional phone or ISDN lines your business still uses, at every site. 

2. List the equipment connected to those lines, including alarms, card terminals, door entry systems and lift phones. 

3. Ask each equipment supplier to confirm in writing that it will work on a digital connection, and to quote for any upgrade. 

4. Speak to your telephone or connectivity provider about migration options and timing. 

5. Arrange any upgrades and test every affected system before the old service is retired. 

Testing deserves the same attention as the upgrade. An alarm that has been reconnected but never triggered proves nothing, so ask each supplier to confirm that a live test has passed. 

Teams Voice solves the smaller part of the job 

Replacing the office phones has the clearest answer. 4TC’s Teams Voice service adds a phone system to a Microsoft 365 plan, so staff can make and receive business calls in Microsoft Teams on compatible computers and mobile devices as well as desk phones, with a single number. Existing numbers can be moved across where supported, and Direct Routing connects Teams to external telephone networks without a hosted telephone system or PBX. 

It takes care of calls and nothing else. Alarm signalling, payment terminals, monitoring connections and other specialist equipment need their own solutions from their own suppliers, so the audit still has to happen. Teams calls also depend on a working internet connection, so the broadband behind them deserves the same attention as the phones. 

A business that knows what depends on its line can choose its own timetable for the change. 

Prepare for the PSTN switch-off with Teams Voice 

If your business still relies on traditional phone lines, find out how 4TC can help you prepare with Teams Voice, or get in touch to talk through your current setup. 

FAQs 

Will my business phone number change? 
Openreach says most businesses can keep their existing number when they move to a digital line, and your provider can confirm this for yours. With Teams Voice, existing numbers can be moved across where supported. 

Do I need Full Fibre to move to a digital phone line? 
No. Digital phone lines are designed to work with Full Fibre where it’s available, and Openreach says other digital services can support a phone line where it isn’t. Your provider can set out the options at your address, and Openreach has a fibre checker for availability. 

How much will the move cost? 
Openreach says costs vary by provider and by the services your business needs. Equipment upgrades belong in the budget, so the supplier quotes from step 3 of the audit are worth having before you commit to a plan. 

How should a business with several sites manage the switch? 
Openreach advises agreeing a transition plan with your provider and starting early to reduce the risk of disruption. Running the audit site by site, as in step 1, gives that plan an accurate starting list.