Replacing Your Business Phone System in Northern Ireland

The Situation Many Businesses Are Facing

If your business phone system was installed more than five years ago and connects to the outside world using ISDN lines, you may now be facing two problems at the same time. Traditional phone lines are being phased out, and many older PBX systems are becoming harder to support. You do not need to panic, but you do need a clear plan.

Openreach's withdrawal of its traditional PSTN-based services, including ISDN, is scheduled for 31 January 2027. Any phone system that relies on ISDN lines needs a migration plan before then. Check your actual line provider and its migration arrangements, because not every legacy service follows an identical cutover process.

Your Two Main Options

Avaya IP Office Replacement

The Avaya IP Office 500 V2 is a common system across Northern Ireland businesses. Many were installed 10 to 15 years ago and have served well. However, several considerations arise around the ISDN withdrawal. Exact options depend on the model, software release and licences installed:

• ISDN interface cards (BRI and PRI) depend on ISDN services that are being withdrawn, so their role needs replacing as part of the migration
• SIP trunks on IP Office need the appropriate SIP trunk licences, and calls between SIP trunks and digital or analogue handsets use voice compression (VCM) channels, so licence count, VCM capacity and the installed software release all need checking
• Avaya 1400 and 9500 series digital handsets are proprietary and cannot be reused on other manufacturers' systems
• Avaya J-series handsets may support SIP, but compatibility with non-Avaya platforms should be tested before assuming reuse is viable
• Older software releases may need upgrading before a SIP migration, which can involve licensing and support-contract costs. Check what your specific system and release support

Full details on Avaya migration options are in our Avaya replacement guide for Northern Ireland.

Panasonic NS700 and NS1000 Replacement

Panasonic systems are common in professional offices, medical premises and hospitality across Northern Ireland. Key migration considerations:

• Panasonic NS700 and NS1000 systems can support SIP trunks when the appropriate activation keys are installed and the software level supports the provider; capability varies by system and configuration, so we check before recommending retention
• KX-DT digital handsets are proprietary and cannot be reused on other systems
• KX-HDV SIP handsets may be reusable, subject to compatibility testing
• DECT systems add migration complexity as DECT handsets are usually system-specific
• Communication Assistant licensing should be checked if call reporting or wallboard features are in use

Full details on Panasonic migration options are in our Panasonic replacement guide for Northern Ireland.

NEC SL1100, SL2100, SV8100 and SV9100 Replacement

NEC systems are another common platform across Northern Ireland businesses and public sector organisations. See our NEC phone system replacement guide for detailed information on SL1100, SL2100, SV8100 and SV9100 migration planning.

Mitel, Siemens, Samsung and Other Systems

The same survey-first approach applies to older Mitel, Siemens (Unify), Samsung OfficeServ, Nortel BCM, Alcatel-Lucent, Toshiba and Cisco phone systems, and to older BT office systems. We list what is connected, including door entry, alarms and analogue extensions, then recommend SIP trunks or a full hosted replacement. Businesses with more than one site can move one site at a time. We replace these systems; this is not a claim of manufacturer-authorised support, and the options depend on the installation and any existing contracts.

For the wider trade-offs between keeping a phone system on site and moving to the cloud, see hosted VoIP versus an on-premises PBX.

Your Numbers and DDI Ranges

Most ISDN30 and PRI systems carry a main number plus a range of direct-dial (DDI) numbers. Before anything moves, we list every number and range on your bills, including any numbers still forwarded from an older supplier, because a number that is missed can stop working when the old line is withdrawn.

• Keeping the existing PBX: SIP trunks can carry the same main number and DDI range into a supported phone system, so extensions and direct numbers keep working.
• Replacing the PBX: the numbers move to the new hosted system, and call routing, hunt groups and voicemail are rebuilt and tested before go-live.
• Number continuity: geographic numbers and ranges can usually be ported, subject to the current provider's checks. We confirm this for your numbers before setting a date, test inbound and outbound calls on each number, and only cancel the old lines once the port has completed.

If your ISDN or phone contract is also ending, see how we review phone contracts before renewal, and for the wider switch-off, our PSTN and ISDN switch-off page.

What Our Assessment Covers

• Identify your existing PBX model and firmware version
• Check SIP support capability and any required hardware or licensing
• Inventory existing handsets and identify which can be reused
• Review your current ISDN lines and SIP trunk requirements
• Check your broadband connection is suitable for SIP/VoIP traffic
• Advise on number porting
• Recommend SIP migration or full cloud replacement based on the findings
• Provide a migration plan with a clear timeline

Engineer's Notes: Replacing a Legacy PBX Without Losing What Works

We have worked with ageing Avaya, Panasonic, NEC and Nortel systems connected to ISDN and PSTN services. The first job is not removing the old system. It is documenting the numbers, extensions, hunt groups, emergency routes, analogue devices, cabling and operational habits that the business still relies on.

Some businesses can retain a suitable PBX and move the external lines to SIP. Others are better served by a hosted or hybrid replacement. Gate openers, intercoms and certain internal phones may continue through an ATA or gateway, subject to compatibility, resilience and any safety requirements.

Large factories and warehouses often have many internal-only or non-essential phones. Charging a full hosted-user licence for every wall phone can make a cloud proposal unnecessarily expensive. Where the platform supports it, we design internal extensions, shared devices, paging or emergency auto-dial phones separately from full office users. SOS buttons, designated-number dialling and fall-detection integrations can also be considered where the approved equipment supports them.

Frequently Asked Questions

What is the ISDN switch-off deadline?

Openreach's withdrawal of its traditional PSTN-based services, including ISDN, is scheduled for 31 January 2027. Phone systems that rely on ISDN lines need either SIP trunks on a suitable existing PBX or a replacement cloud phone system before then. Check your actual line provider and its migration arrangements, because not every legacy service follows an identical cutover process.

Can I keep my existing Avaya or Panasonic handsets?

It depends on the handset model. Some handsets support SIP and can potentially be reused. Proprietary digital handsets (Avaya 1400/9500 series, Panasonic KX-DT series) cannot be reused on a different manufacturer's platform. We check which handsets you have and advise on reuse or replacement as part of the assessment.

What is the difference between SIP trunking and full cloud VoIP?

SIP trunking replaces the ISDN lines while keeping the existing PBX in place. Full cloud VoIP replaces the PBX entirely with a hosted platform. SIP migration is lower cost if the PBX is in good condition and supports SIP. Full replacement is simpler to manage long term and avoids ongoing hardware maintenance.