PSTN Switch-Off | How to Migrate Your Business to VoIP

Understanding the UK PSTN Switch-Off

The Public Switched Telephone Network (PSTN) is the UK's traditional copper telephone network — the infrastructure that has carried analogue voice calls for over a century. BT's Openreach division is systematically decommissioning this network and replacing it with a full-fibre and IP-based infrastructure. The process is called the PSTN switch-off.

For businesses, this means that all voice services running on copper lines — including PSTN lines, ISDN2, and ISDN30 — will eventually cease. The only path forward is VoIP: internet-based telephony that transmits calls as data rather than analogue signals.

What Has Already Happened

The PSTN switch-off has been progressing since BT announced the programme in 2019. Key milestones already reached:

• ISDN30 lines have been ceased in the majority of UK exchange areas
• New PSTN and ISDN orders are no longer accepted in most areas
• Openreach has completed full-fibre (FTTP) deployment in a growing proportion of UK premises
• The "Stop Sell" designation has been applied to legacy services in areas where FTTP is available

What Businesses Need to Do

Step 1: Audit Your Telephony Dependencies

Before migrating, establish exactly what you have. This audit should cover:

• All PSTN and ISDN lines — how many, what numbers, which office locations
• Alarm lines (intruder alarms, fire alarms) — these may be on separate PSTN lines
• Lift emergency phones — regulatory requirement, often on dedicated lines
• Fax machines — still used in some sectors; replaceable with internet fax services
• Payment terminals — some older card terminals use PSTN; check with your payment provider
• CCTV dial-out lines — older CCTV systems may use PSTN for remote monitoring

The non-voice dependencies are the most commonly overlooked aspect of PSTN migration planning and the most frequent source of post-migration problems.

Step 2: Assess Your Internet Connectivity

VoIP calls run over your internet connection. The quality of your connectivity directly affects call quality. Assess:

• Current broadband speed and type (FTTC, FTTP, leased line)
• Contention and consistency (how much variation in performance during business hours)
• Latency and jitter (more important than raw speed for VoIP quality)
• Whether your current connection can support your expected concurrent call volume

As a guide, each VoIP call uses approximately 100 kbps. Ten concurrent calls need 1 Mbps dedicated to voice. Most modern business broadband connections can handle this, but quality matters as much as capacity.

Step 3: Choose a VoIP Provider

The PSTN switch-off creates a compelling prompt to evaluate the VoIP market rather than defaulting to whatever your existing carrier (usually BT) proposes. Independent providers such as Gamma Horizon, 3CX, and Microsoft Teams Phone typically offer better features at lower cost than incumbent carrier VoIP products.

Evaluate providers on: feature set vs. your requirements, uptime SLA, support quality, pricing over the full contract term, and migration support included. AMVIA provides this comparison as a structured, no-obligation service.

Step 4: Plan Number Porting

Your existing phone numbers — including 01, 02, 03, and 0800 numbers — can be transferred to your new VoIP provider through number porting. The process takes approximately 5–10 working days. Plan the porting carefully:

• Complete new VoIP system setup and testing before porting
• Schedule porting during a low-traffic period (e.g., end of day Friday)
• Confirm porting completion before decommissioning old lines

Step 5: Hardware and Endpoint Decisions

Traditional PSTN phones do not work with VoIP. Decide on endpoints:

• IP phones: Purpose-built VoIP desk phones (Yealink, Cisco, Poly). Cost £80–£200 per device.
• Softphones: Apps on existing laptops and desktops. No hardware cost.
• Mobile apps: VoIP apps on smartphones. No additional hardware cost.
• ATAs: Analogue telephone adaptors that allow existing phones to work on VoIP. Cost £30–£80 per device.

Step 6: Address Secondary Line Dependencies

For each secondary line identified in the audit — alarm, lift, fax — confirm a migration path:

• Alarm and CCTV: Contact the monitoring company or installer for VoIP-compatible alternatives
• Lift phones: Contact the lift manufacturer for IP-compatible emergency phone options
• Fax: Replace with an internet fax service (e.g., eFax) or disable if no longer required
• Payment terminals: Contact your payment provider for a modern IP-based terminal

AMVIA manages the complete PSTN migration process for UK businesses — handling all six steps as a coordinated, managed service to ensure no communications disruption during the transition.