How much does the PSTN switch off cost a UK business?
Most UK businesses pay between £10 and £20 per user per month for a modern cloud replacement, and typically reduce total telephony spend by 20-40% versus legacy PSTN and ISDN. Hardware, cabling and specialist device replacements (alarms, lifts, EPOS) are the main one-off costs.
Cost Comparison by Business Size
Typical monthly costs before and after migrating off PSTN and ISDN
Sole trader / micro (1-5 users)
Legacy cost
£25-£60 / month
Digital replacement
From £9.95 per user / month
ISDN / PSTN risk
Low - usually single analogue line
Recommended path
Cloud VoIP (SelectVoice Essentials)
Often break-even or a small saving, plus mobile and desktop apps.
Small business (6-25 users)
Legacy cost
£150-£500 / month
Digital replacement
From £12.95 per user / month
ISDN / PSTN risk
Medium - often 2-4 ISDN2 channels or a small PBX
Recommended path
Cloud VoIP or Teams Direct Routing
Typical 20-40% reduction in line rental and call costs.
Mid-market (26-100 users)
Legacy cost
£600-£3,000 / month
Digital replacement
SIP from £5 / channel, or bundled cloud seats
ISDN / PSTN risk
High - ISDN30, multi-site, legacy PBX, alarm and lift lines
Recommended path
SIP Trunking (retain PBX) or full cloud migration
30-50% saving on line rental, plus contact-centre features included.
Enterprise / multi-site (100+ users)
Legacy cost
£3,000+ / month
Digital replacement
Custom - typically tiered per site and channel
ISDN / PSTN risk
Critical - business continuity, compliance, resilience
Recommended path
SIP Trunking with failover + Teams Direct Routing
Consolidated billing, geographic resilience, AI call analytics.
What the Switch Off Actually Affects
A checklist of the services and devices that break when PSTN is retired
Phone lines (PSTN / ISDN)
Impact
Stop working after 31 January 2027. New PSTN lines already unavailable in stop-sell areas.
Action
Migrate to VoIP, SIP Trunking or Teams Direct Routing.
Broadband on copper (ADSL, FTTC voice)
Impact
The voice element of a line is being retired; broadband must move to SoGEA or FTTP.
Action
Upgrade to SoGEA or Full Fibre (FTTP).
Alarms, lifts and telecare
Impact
Many older monitored alarms and lift phones rely on an analogue line and will fail.
Action
Replace with IP-enabled units or a dedicated resilient line.
Card payment terminals (EPOS)
Impact
Dial-up card machines will no longer authorise transactions.
Action
Move to IP or 4G-enabled terminals before migration.
Fax and franking machines
Impact
Analogue signalling breaks. Fax over IP is unreliable.
Action
Replace with email-to-fax, secure document portals or IP-native devices.
The Hidden Cost of Waiting
Where late migrations quietly add thousands to the bill
- Emergency out-of-hours engineer callouts once the deadline passes.
- Lost calls and abandoned enquiries during unplanned downtime.
- Rushed hardware procurement at premium pricing in late 2026.
- Data-cabling upgrades needed to support IP handsets on older sites.
- Alarm re-certification and insurance implications for unmonitored premises.
Cost & Impact FAQs
Answers to the questions UK businesses ask most