7 steps to prepare your business for the UK PSTN/ISDN switch off (2025 update)

Openreach now plans to switch off the existing PSTN/ISDN network by 31 January 2027. At the same time, BT and Openreach have repeatedly urged businesses to migrate to all-IP/VoIP services as soon as possible, and in guidance for business customers, they recommend migrating early – businesses are encouraged to move before the end of December 2025 to avoid risk.

Following a series of incidents affecting some telecare devices, in December 2023, the government and industry agreed a temporary pause on non-voluntary migrations. A PSTN charter to protect vulnerable customers was introduced, and the final switch-off date was moved to January 2027.

Openreach is actively supporting businesses and households in the transition to digital landlines (voice delivered over broadband) and is publishing guidance, toolkits, and regional plans as the programme progresses. Businesses should not wait until the last moment, as some communications providers have earlier cut-off dates. A planned migration is the safest, most economical approach.

You’ll see the terms SIP and VoIP a lot. Here’s a short, executive summary:

• VoIP (Voice over Internet Protocol) is the technology that actually carries voice calls over the internet instead of copper lines. Put simply, when someone rings you on a VoIP system, their voice is sent as data packets across your internet connection. VoIP replaces the old ‘analogue’ call transport with digital transport.
• SIP (Session Initiation Protocol) –  think of SIP as the rules for setting up and finishing phone and video calls. SIP controls who is talking to who, where to route a call, and how to add features such as hold, transfer or voicemail. If VoIP is the vehicle, SIP is the traffic control system that directs journeys.

Why this matters: moving to SIP/VoIP means phone calls become software-driven rather than tied to physical copper wiring. That enables new capabilities (integrations to CRM, call analytics, home-worker support), but it also means call quality and resilience depend on your internet and security setup.

Why it matters

As digital voice and video run on your internet connection, poor connectivity can mean poor call quality, dropped calls and unhappy customers.

What to check

• Test your current bandwidth and latency during your busiest hours.
• Is fibre available to your site? Do you have a business-grade SLA and static IPs where needed?
• Consider dual connectivity (a fibre primary line with 4G/5G or secondary fibre as back-ups) to allow the business to stay online if your connection fails.
• Consider Quality of Service (QoS) or traffic-prioritisation options to keep voice packets flowing even during heavy data use.

Action: Commission a short connectivity audit that includes current capacity, shortfall, recommended upgrades and cost estimates.

Why it matters

Many systems rely on PSTN in ways you may not expect: alarms, lift emergency lines, PDQ/Epos terminals, building entry systems and some fax/monitoring systems.

What to check

Create a simple inventory – list phone numbers, ISDN/analogue lines, PBX(s), alarm lines, card machines, fax machines, lift/emergency lines.

• Identify single points of failure and any services used by vulnerable customers (telecare, call-out alarms).
• Mark items that cannot be migrated automatically (some alarms or bespoke kit need vendor replacement or converters).

Action: Request a vendor audit (either an onsite review or a remote inventory) and an upgrade plan with clear costs and timelines.

What’s available:

• Hosted VoIP (cloud PBX / UCaaS): ideal for distributed teams, quick to deploy, features included (ring groups, voicemail to email, mobile apps).
• SIP trunking: lets you keep an existing on-premises PBX but route calls over the internet –  good when a significant PBX investment exists.
• Unified platform (Microsoft Teams): if you already use Teams, adding phone capabilities can simplify licences and workflows.

Considerations: Compare total cost of ownership (licence fees + handset costs + broadband), vendor SLAs, integration with CRM, and number porting. Ask about the provider’s migration support and whether they handle edge cases such as telecare or PDQ machines.

Ideally your plan should be pragmatic and risk-based:

• Start with a pilot: migrate a small team or single site first. Validate call quality, integrations and failover.
• Phased migration: move lower-risk lines first, keep critical services until you’ve proven failover works.
• Stakeholder map: include IT, operations, facilities (for alarms/lifts), finance (payment terminals), and HR (user training).
• Timelines and decision gates: set clear milestones (audit complete, pilot live, staff training done, full cutover).

Action: Approve a phased budget and a project owner. Make sure the migration has an escalation path and a fall-back plan. If you want a fully managed rollout, an MSP such as Curveball Solutions will project-manage the migration end-to-end, from procurement to cut-over and onboarding.

Testing areas:

• Call quality metrics: MOS, jitter, packet loss thresholds – vendors should provide test results for sample calls.
• Business flows: test inbound call routing, voicemail, transfers, CRM screen-pop for sales/finance.
• Payment machines and alarms: confirm PDQ/EPOS and alarm providers work over the new setup (or provide a compliant adapter).
• User acceptance: train a pilot group and collect feedback.

Action: Speak to your vendor or MSP about pre-launch testing and the provision of ongoing optimisation services to ensure call quality remains high.

Why it matters

VoIP systems are exposed to IP-network threats (toll fraud, eavesdropping, DDoS), and moving voice calls to IP changes your threat model.

Key measures

• Deploy session border controllers (SBCs) or provider-managed equivalents to protect SIP sessions.
• Use encrypted signalling and media (TLS / SRTP) where supported.
• Harden admin interfaces and use role-based access control.
• Patch and monitor devices and servers; log call activity to detect anomalies.
• Train users on phishing and secure remote working (home routers are often weak points).

Action: Include security requirements in your procurement, such as encryption, SBC, logging and incident response time. Curveball Solutions can provide security advice and implement technical controls on your digital telecom solution.

Your customers don’t want to be told ‘we’re offline’ but with a robust failover plan your business can stay connected.

• Secondary internet (4G/5G or alternate fibre provider) for automatic failover.
• Cloud call routing: numbers hosted in the cloud can be re-routed to mobiles, alternate offices or contact centres instantly.
• Geographic redundancy: avoid single-site PBX/servers; use cloud vendor redundancy where possible.
• Regular testing: schedule quarterly failover drills so everyone knows the process.

Action: Build failover into your requirements and budget for at least one independent backup connection. Curveball Solutions can design and implement failover routing and run regular tests so you can demonstrate continuity to stakeholders and auditors.

• Final switch-off date: Openreach states the existing PSTN/ISDN network will be withdrawn by 31 January 2027. Openreach
• Act early where possible: BT is urging businesses to migrate to all-IP as soon as practical and recommends migrating before the end of December 2025 where possible to reduce risk.
• Serious incidents prompted the pause: government attention and industry investigations followed some telecare failures; the pause and resulting checks have shaped how and when non-voluntary migrations resume.

Quick checklist (what to approve this month)

• Approve a telecoms infrastructure audit (inventory of PSTN dependencies).
• Budget for required connectivity upgrades and at least one backup connection.
• Authorise a pilot migration for a single team or site.
• Arrange a meeting with a reliable MSP (ask for a timeline, costs and responsibilities).

Curveball Solutions can assist with a current communications audit and provide strategic advice, along with a recommended timeline and budget. We’ll also provide a clear migration route that minimises disruption and protects any vulnerable services.

The final PSTN/ISDN switch-off is now scheduled for 31 January 2027, but industry guidance (and common sense) means migrating earlier is wise, mainly to avoid hidden costs, security exposure and disruption to critical services. A measured, phased migration will protect customers and staff, and offer the added benefit of modern features and operational efficiencies once you transition to SIP/VoIP.