Challenges
Preparing for the PSTN switch-off
Analogue and ISDN lines are retired on 31 January 2027. Every line still on them has to move, including the alarm and the lift, and your numbers have to keep working through the move.
The challenge
Your phones may already be on a modern system, but the lines behind them, the alarm, the lift phone, the door entry panel and the card terminal often are not. Openreach is retiring the analogue and ISDN network, with 31 January 2027 as the date the switch-off completes, and no new analogue line can be ordered now. The job is to find every line, decide what replaces each one, and move it without losing a number.
If it is left
A line nobody remembers is the one that fails. After the date, business lines that have not migrated are not guaranteed to work, and a line that fails before it cannot be replaced like for like. The visible risk is a phone that stops ringing; the quieter ones are an alarm that no longer signals, a lift phone that no longer reaches a monitoring centre, and a card terminal that stops taking payments. Openreach has also said the cost of the old lines rises as the date approaches, so waiting costs money as well as risk.
What good looks like
Every number ported to a digital service and ringing where it should, the alarm and lift lines on a replacement the alarm company has tested, nothing left on a line that is about to be withdrawn, and a connection with capacity for the calls as well as everything else. Most businesses end up with fewer lines, lower rental and phones that follow people rather than desks.
What to do first
Before you call anyone
Get the phone bills out
Every line you pay for is on a bill, usually from more than one supplier. List each number and line rental, including the ones you cannot place.
Walk the building
Look for anything with a phone socket behind it: the alarm panel, the lift car, the door entry panel, the fax, the franking machine, the card terminal, the server room dial-up modem.
Ask your alarm and lift companies
Ask each one, in writing, what their equipment will run over after the switch-off and whether they will supply the replacement. Their answer sets your plan.
Check your phone system's age
A system that supports SIP can be kept and connected over the internet. One that cannot, or that is out of manufacturer support, is usually replaced rather than patched.
Note which numbers matter
The ones on the van, the letterhead, the website and Google. Those must port; the rest can be rationalised.
To see what still runs on the old phone network, take the PSTN switch-off check: ten questions, and a list of what has to move before the switch-off. To see which broadband an address can get, enter its postcode in the broadband checker.
What we would do first
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Audit every line and number
The lines and numbers you have today and where each one goes, including the ones nobody remembers: alarms, lifts, door entry, fax and card terminals.
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Decide what replaces each one
Hosted voice, SIP or Microsoft Teams for the phones; a digital service for the alarm and lift lines; broadband or ethernet to carry it all.
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Port the numbers
Existing numbers moved to the new service so customers keep calling the number they know.
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Migrate before the date
ISDN and analogue lines moved to digital services, with each number routed to the right people and hours.
How we approach it
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Audit
We check the bills, the comms cupboard and the building, because the lift phone is rarely on anyone's list, and produce one list: every line, what runs over it, who supplies it and which numbers must survive.
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Choose the replacement per line
Phones move to hosted voice (Odyssey Voice), to SIP trunks if your system supports them, or to Microsoft Teams calling through Direct Routing. Alarm, lift and door-entry lines move to a digital service designed for them, with analogue converters where legacy equipment must stay.
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Check the connection
Calls need a connection with capacity to spare. We check what your address can get and recommend business broadband (SoGEA or full fibre FTTP), a leased line where the site cannot be offline, and a 4G or 5G backup so the phones keep ringing if the line fails.
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Port and migrate, line by line
New services are set up and tested while the old lines still work, numbers are ported on agreed dates, the alarm and lift companies confirm their equipment on the new service, and the old lines are ceased only when the replacements are proven.
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Tidy up
Rental on lines nobody uses stops, each number is routed to the right people and hours, and the service desk takes over changes from then on.
The services that apply
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Telecoms audit and PSTN migration
The audit as a project: every line, number and contract found, including the alarm and lift lines, a replacement chosen for each, and the migration done before the date.
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Telephone lines and numbers
The porting and the replacement lines themselves, including a digital service for the alarm, lift and card-terminal lines that are not phones.
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Hosted voice and SIP
The usual destination for the phones: a hosted system with no cabinet to replace, or SIP trunks that keep a phone system you already own.
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Microsoft Teams
For a business that already lives in Teams, the numbers can move into Teams through Direct Routing instead of onto a separate phone system.
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Business broadband
The replacement lines run over the internet, so the connection has to carry calls as well as everything else; a line-rental saving often pays for the upgrade.
How you would buy it
Every hour we work falls under one of four engagement models. These are the ones that fit this situation; How we work compares all four.
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02
Fixed price
A defined piece of work or project
The audit, the porting and the migration are surveyed and priced as a fixed sum before we start, with a project manager where several sites move, and any overrun is ours.
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03
Retainer
The way most of our clients work with us
After the move, re-routing, new numbers and opening-hours changes are pre-authorised within your retained hours and done by the service desk there and then.
Who you would work with
An account manager
Your first conversation and the plan, with the dates set around your contracts and your operations.
A project manager, where several sites move
Owns the dates, the porting orders and the alarm and lift companies, so nothing is a surprise on the day.
Our telephony engineers
Odyssey employees, never subcontracted, who set up the new service, port the numbers and test each line before the old one goes.
The service desk
Answers within three rings from then on, and makes the day-to-day changes.
A client who has been here
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Client story, Construction and quarrying
Dunhouse Quarry
A hosted Mitel system and SIP lines to sustain higher call volumes across sales and administration as the quarry expanded.
Read the story →
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Guide
The ISDN and PSTN switch off and its effects on my business
Analogue and ISDN lines are being retired. What that means for your phones, alarms and lifts, and how to plan the move to IP.
Read the guide →
Questions people ask
When is the PSTN switch-off?
Openreach is retiring the PSTN and ISDN, with 31 January 2027 as the date the switch-off completes; the date moved from December 2025, and Openreach has said it will not move again. New analogue lines can no longer be ordered, so a line that fails now cannot be replaced like for like.
What happens if we miss the date?
A business line that has not migrated is not guaranteed to keep working after the date, and anything that runs over it stops with it. If you are reading this after January 2027 and still have a line on the old network, the first step is the same: find every line and move it now.
Will we keep our phone numbers?
Yes. Existing numbers are ported to the new service, whether that is hosted voice, SIP or Microsoft Teams, so customers keep calling the number they know. We audit every number first so none is missed.
Does the switch-off affect alarms, lifts and card terminals?
Yes. Any technology running over PSTN or ISDN lines stops working, which can include alarm systems, lifts, door entry and card terminals. Each one needs a digital replacement before the date, and we coordinate with the alarm or lift company.
Can we keep our existing phone system?
Possibly. If it supports SIP, we can connect it with SIP trunks; if not, hosted voice or Microsoft Teams replaces it. Some legacy equipment can be kept with analogue converters.
Will our internet connection cope?
It may need upgrading so it has capacity for calls as well as everything else. We check what your address can get and recommend broadband or a leased line to carry it, and a 4G or 5G backup where the phones cannot be allowed to stop.
How long does it take?
It is set by the port and by any new connection, both outside our control: a number port typically takes 7 to 14 working days, new business broadband 10 to 15 and a leased line 60 to 90. We give you the dates at the audit and work the plan back from them.
What does it cost?
The migration is priced as a fixed sum after the audit, and the new services are a monthly charge. Most businesses find the rental on lines they no longer need offsets a good part of it; we show you both numbers before you commit.
Talk to a human about the PSTN switch-off
Call and we answer within three rings. Or tell us what you need and we will call you back at any time.