PSTN and ISDN Switch Off: What Northern Ireland Businesses Need to Do

The UK's traditional analogue phone network (PSTN) and ISDN lines are being switched off. This is not a rumour or a distant plan. Openreach has been stopping new PSTN sales since September 2023 and the full network shutdown completes by January 2027. Every business in Northern Ireland still using traditional phone lines, ISDN, or analogue services over copper needs to move to a digital alternative.

What Is Actually Happening

• PSTN (Public Switched Telephone Network) is the traditional analogue phone system that has existed for over 100 years. It is being decommissioned.
• ISDN (Integrated Services Digital Network) is the digital line technology that replaced analogue for businesses in the 1990s. It is also being decommissioned.
• All voice services will run over IP (internet protocol) after the switch-off. This means VoIP, SIP trunking, or hosted cloud phone systems.

This affects every business that uses a traditional phone line, an ISDN-connected PBX, an analogue fax machine, a dial-up alarm system, or any device that communicates over the old copper phone network.

What Stops Working

• Traditional analogue phone lines (the ones that work during a power cut)
• ISDN2 and ISDN30 lines connected to PBX systems
• Fax machines connected to analogue lines
• Alarm systems that dial out over PSTN to a monitoring centre
• Payment terminals that use phone lines (older PDQ machines)
• Door entry systems connected to phone lines
• Lift emergency phones on analogue lines
• Redcare or similar alarm signalling over PSTN

What Replaces It

Voice services move to VoIP (Voice over Internet Protocol). This means your phone calls travel over your broadband connection instead of a separate copper pair. In practice, this means one of:

• Hosted cloud phone system your entire phone system runs in the cloud. Desk phones, mobile apps, and softphones all connect via broadband. No hardware PBX on your premises. This is what most small businesses should move to.
• SIP trunking if you have an existing PBX that supports SIP (most modern ones do), SIP trunks replace your ISDN lines. The PBX stays, but the lines become internet-based.
• Analogue telephone adapter (ATA) for devices that must remain analogue (some alarms, some fax machines), an ATA converts the analogue signal to VoIP. This is a stopgap, not a long-term plan.

What Northern Ireland Businesses Should Do Now

1. Check what you have. Look at your phone bill. If it mentions PSTN lines, ISDN2, ISDN30, or analogue line rental, you are affected.
2. Check your alarm system. If your intruder alarm or fire alarm dials out over a phone line, it will stop working after the switch-off. Contact your alarm provider or ask us to check.
3. Check card machines. Older PDQ terminals that dial over a phone line need replacing with broadband or 4G-connected models.
4. Plan your phone system migration. Do not wait until your line is switched off. Plan the move to VoIP on your timeline, not Openreach's.
5. Check your broadband. VoIP depends on reliable broadband. If your connection is slow, unstable, or has no failover, fix that before moving your phones to it.
6. Keep your numbers. Existing phone numbers can be ported to VoIP. This takes 5-10 working days and should be planned, not rushed.

Common Concerns

Will my phone work during a power cut?

Traditional analogue phones were powered by the phone line itself, so they worked during mains power failures. VoIP phones depend on your broadband and router, which need mains power. If power resilience is critical, you need a UPS (battery backup) on your router and a 4G failover connection. This is straightforward to set up but needs planning.

Will call quality be as good?

On a properly configured broadband connection with QoS enabled on the router, VoIP call quality is as good as or better than ISDN. Problems arise when broadband is overloaded, Wi-Fi is poor, or the router does not prioritise voice traffic. All of these are fixable.

Can I keep my existing phone numbers?

Yes. All UK geographic numbers (028 in Northern Ireland) can be ported to VoIP. The porting process takes 5-10 working days. Your numbers stay the same. Customers will not notice any difference.

What if I have a PBX system?

If your PBX supports SIP trunking, you can keep it and replace the ISDN lines with SIP trunks. If it is an older system that only supports ISDN, you have a choice: replace the PBX with a cloud phone system, or add a media gateway that converts SIP to ISDN (expensive and fragile as a long-term plan). For most small businesses, moving to a hosted cloud system is simpler and cheaper than maintaining old hardware.

Do Not Wait for Your Provider to Contact You

Some businesses are waiting for BT or Openreach to tell them what to do. That communication is often a generic letter that arrives late and offers an expensive like-for-like replacement. You will get a better outcome by planning the move yourself (or asking someone to plan it for you) rather than reacting to a deadline letter.

Replacing Older Avaya, Panasonic and NEC Phone Systems

If your business uses an older PBX such as Avaya IP Office, Panasonic NS700 or NEC SL2100/SV9100, the switch-off may mean SIP migration or a full move to cloud VoIP. Both options exist and which one is right depends on your hardware, firmware and licence situation.

• PBX phone system replacement in Northern Ireland - full migration hub covering all major platforms
• Avaya phone system replacement Northern Ireland - IP Office 500 V2 migration options
• Panasonic PBX replacement Northern Ireland - NS700 and NSX migration guide
• NEC phone system replacement Northern Ireland - SL2100, SV8100 and SV9100 options