A multi-line phone system lets your business handle multiple calls simultaneously – routing them to the right person, department, or voicemail without callers hitting a busy signal. In 2026, this means a cloud VoIP system with virtual extensions rather than physical phone lines plugged into a box on the wall.
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The UK’s PSTN switch-off retires every analogue and ISDN phone line by January 2027, making traditional multi-line hardware obsolete. This guide covers how modern multi-line systems work, what they cost, and which providers offer the best value for UK businesses.
- Cloud multi-line plans start from £7/user/month - bOnline’s entry tier (ex VAT, 100 outbound landline minutes), with no PBX hardware to buy upfront
- Cloud systems have no ISDN-style line cap - each user gets a virtual extension, not one of a fixed number of physical channels (ISDN2 gives 2 per line, ISDN30 up to 30)
- Hardware cost drops to £0 - cloud systems run over your existing broadband, with IP desk phones optional at a separate hardware price
- The UK PSTN switch-off completes by January 2027 - retiring every analogue and ISDN line, so traditional multi-line hardware must be replaced
What Is a Multi-Line Phone System?
A multi-line phone system allows a business to manage two or more phone calls at the same time across multiple extensions, departments, or locations using a single service.
Traditional multi-line systems worked by splitting a physical phone line into multiple extensions using hardware (PBX boxes, key systems, or ISDN connections). Each line required a separate cable, and adding more lines meant engineering visits and hardware purchases.
Modern multi-line systems are cloud-hosted. Each user gets a virtual extension that works on their desk phone, laptop, or mobile app. There are no physical lines to split – everything runs over your broadband connection. Adding a new line takes seconds in an online admin portal, not days waiting for an engineer.
The core functions remain the same: handling multiple simultaneous calls, transferring between extensions, putting callers on hold, and routing calls to departments. The technology delivering those functions has fundamentally changed.
Traditional vs Cloud Multi-Line Systems
Cloud multi-line systems eliminate the upfront hardware cost of a traditional PBX, scale instantly, and are unaffected by the PSTN switch-off deadline of January 2027.
| Feature | Traditional Multi-Line (PBX/ISDN) | Cloud VoIP Multi-Line |
|---|---|---|
| How it works | Physical lines split by hardware in your office | Virtual extensions over broadband |
| Number of lines | Limited by hardware (2, 4, 8, or 16 typical) | Unlimited – add as many as you need |
| Upfront cost | An upfront hardware and installation quote | Use existing devices; optional IP phones priced separately |
| Per-line cost | ISDN line rental per channel, plus maintenance | £7-£30/user/month (plus VAT on some plans) |
| Adding lines | Engineer visit and lead time | Self-service, instant |
| Remote access | Usually needs a VPN or extra equipment | Built-in – any internet connection |
| PSTN switch-off | Stops working January 2027 | Completely unaffected |
| Features included | Basic – extras cost per module | IVR, recording, analytics and video on mid-tier plans; entry plans hold some back |
If your business currently uses a traditional multi-line system with BT or ISDN lines, you need to migrate before January 2027. Most cloud providers can port your existing numbers, so your customers continue calling the same numbers. Timings depend on your current provider and the type of number, and ISDN ranges can take longer.
Best Multi-Line Phone Systems for UK Businesses
RingCentral, bOnline, Dialpad, and GoTo Connect are the leading multi-line cloud phone systems for UK SMEs, with plans starting from £7 per user per month (ex VAT).
| Provider | From (per user/month) | Line limit | Best For |
|---|---|---|---|
| RingCentral | £7.99 (2-19 users, annual billing) | No fixed line cap | Growing businesses needing 500+ app integrations |
| bOnline | £7 (ex VAT) | No fixed line cap | Small businesses wanting a low-cost entry |
| Dialpad | £12 (annual billing) | No fixed line cap | Teams wanting AI call transcription and summaries |
| GoTo Connect | Quote-based | No fixed line cap | Businesses calling landlines in 50+ countries |
| Vonage | £10 (outbound calls metered) | No fixed line cap | Sales teams needing supervisor tools (whisper/barge on higher tiers) |
| 8×8 | Quote-based | No fixed line cap | Mid-sized teams with heavy international calling |
Cloud VoIP gives each user a virtual extension rather than a fixed pool of physical lines, so there is no ISDN-style channel limit. Check each plan’s terms for any concurrent-call or fair-use cap, and remember your broadband bandwidth sets the practical ceiling.
How Many Lines Does Your Business Need?
With cloud VoIP, you do not need to calculate “lines” – every user gets their own extension, so there is no fixed pool of physical lines to size. The old concept of counting phone lines is largely obsolete.
Traditional multi-line systems forced businesses to estimate peak call volumes and buy enough physical lines to handle them. Too few lines meant missed calls; too many meant wasted money. This was one of the most common pain points with legacy systems.
Cloud VoIP eliminates this problem entirely. Each user has their own extension, and capacity is not tied to a physical line count. The main limiting factor is your broadband connection – each active call uses approximately 100kbps of bandwidth.
| Business Size | Users | Broadband Needed | Estimated Monthly Cost |
|---|---|---|---|
| Micro (sole trader to 4 staff) | 1-4 | Standard broadband (10Mbps+) | £7-£80/month total |
| Small (5-19 staff) | 5-19 | Fibre broadband (30Mbps+) | £50-£300/month total |
| Medium (20-99 staff) | 20-99 | Business fibre (100Mbps+) | £200-£1,500/month total |
| Multi-site | 50+ | Fibre at each location | Quote-based |
For any office with standard fibre broadband (30Mbps+), you can comfortably support 30+ simultaneous VoIP calls. Even basic broadband handles 5-10 concurrent calls without quality issues. If your business regularly has 50+ staff on calls at once, consider dedicated business fibre or SIP trunking for guaranteed call quality.
Key Features of Modern Multi-Line Systems
Cloud multi-line systems include auto-attendant, ring groups, call queuing, voicemail-to-email, call recording, and mobile apps on most plans – features that cost extra with traditional hardware.
When multi-line systems ran on physical hardware, every feature beyond basic call handling required an additional module or licence. Cloud providers bundle most of these into the monthly subscription:
- Auto-attendant (IVR) – “Press 1 for Sales, 2 for Support” routing without a receptionist
- Ring groups – incoming calls ring the whole sales team simultaneously until someone answers
- Call queuing – holds callers with music and position announcements during busy periods
- Call recording – automatic recording for compliance, training, or dispute resolution
- Voicemail-to-email – missed call recordings delivered to your inbox, often with AI transcription
- Call analytics – dashboards showing call volumes, wait times, missed calls, and peak hours
- Mobile app – your business number on your personal phone, with separate call history
- Video conferencing – built-in video meetings (up to 300 participants on RingCentral Standard, Premium and Ultimate, and up to 200 on Vonage; Dialpad’s standard tier is far smaller)
- CRM integration – caller info from Salesforce, HubSpot, or Zoho pops up when the phone rings
- AI transcription – automatic call notes and summaries (Dialpad; RingCentral sells AI Conversation Expert as a £48/user add-on)
Most of these features come with mid-tier plans from the major providers, but entry plans hold some back. RingCentral Essentials excludes video meetings and call recording, and Vonage Express excludes call recording and CRM integrations. Check the plan, not just the provider.
How Much Does a Multi-Line Phone System Cost?
Cloud multi-line systems cost £7-£30 per user per month with no hardware investment. A 10-person office pays a monthly bill based on the selected plan and number of users, compared with a large upfront outlay for equivalent traditional hardware.
| Cost Element | Cloud VoIP | Traditional Multi-Line PBX |
|---|---|---|
| Hardware | £0 (use existing devices) or a separate quote for each IP desk phone | A separate quote for the PBX unit and installation |
| Monthly per user | £7-£30 | ISDN line rental per channel, plus maintenance |
| Calls | Unlimited UK calls on mid-tier plans; entry plans cap or meter outbound minutes | Per-minute billing on most tariffs |
| Installation | Self-setup, same day | Engineer required, quoted per site |
| Adding users | Free – add online instantly | Additional hardware and licences quoted separately |
| Maintenance | Included | Maintenance contract or per-callout charges |
Example: 10-person business. A cloud multi-line system with bOnline costs £70/month ex VAT (10 users x £7, each with 100 outbound landline minutes). With RingCentral Standard, which adds video conferencing and integrations, it is about £150/month on annual billing (10 users x £14.99). An equivalent traditional PBX setup needs an upfront hardware and installation quote, plus separate recurring charges in ISDN line rental and maintenance – and it will stop working when the PSTN shuts down.
Most cloud providers offer volume discounts for larger teams and cheaper annual billing. RingCentral Essentials, for example, is £7.99 per user on annual billing versus £12.99 billed monthly for teams of 2 to 19, and the per-user price of its other plans falls again at 20 and 100 users.
Our Verdict
Every UK business using a traditional multi-line phone system should migrate to cloud VoIP before the January 2027 PSTN deadline. Cloud systems are cheaper, more flexible, and include features that old hardware never offered.
For a small UK business, bOnline offers a simple, low-cost multi-line setup from £7/user ex VAT. For businesses that need integrations, video conferencing, and advanced analytics, RingCentral (from £7.99/user for teams of 2 to 19 on annual billing) is the most complete platform. Teams with heavy international calling should look at GoTo Connect (free calls to landlines in 50+ countries) or 8×8 (unlimited calling to up to 47 countries on its higher tiers).
If you are still using a traditional multi-line system connected to BT lines or ISDN, start your migration now. Porting and installation timings vary by provider and number type, and every month you delay is another month paying premium rates for a system approaching end-of-life.
Read our full comparison of business phone systems or browse individual reviews: Dialpad, Vonage, Google Voice, NBC Cloud Voice. For businesses needing physical handsets alongside their cloud system, see our guide to office cordless phones.
