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.
FREE QUOTE COMPARISON
Compare Telephone System Quotes from Trusted Suppliers
✓ Save up to 40% on business phone costs
100% free • No obligation • Takes under 2 minutes
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 systems cost 50-70% less than traditional PBX - eliminating hardware investment while improving scalability and features
- Top 6 systems handle 10-500+ concurrent calls - scaling from small offices to enterprise call centers seamlessly
- Auto-attendant reduces call handling time by 35% - routing calls efficiently without human operator intervention during peak hours
- Most businesses need 1.5-2x lines per employee - accounting for concurrent calls, voicemail, and departmental routing requirements effectively
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 cost 60-80% less than traditional hardware 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 | £1,000-£10,000+ for hardware | £0-£150 (IP phones optional) |
| Per-line cost | £15-£30/month per ISDN channel | £7-£25/user/month (all-inclusive) |
| Adding lines | Engineer visit, 1-2 week lead time | Self-service, instant |
| Remote access | Not possible without VPN | Built-in – any internet connection |
| PSTN switch-off | Stops working January 2027 | Completely unaffected |
| Features included | Basic – extras cost per module | Full suite: IVR, recording, analytics, video |
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 within 5-10 working days, so your customers continue calling the same numbers.
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.
| Provider | From (per user/month) | Simultaneous Calls | Best For |
|---|---|---|---|
| RingCentral | £12.99 | Unlimited | Growing businesses needing 300+ app integrations |
| bOnline | £7 | Unlimited | Small businesses wanting the lowest cost entry |
| Dialpad | £12 | Unlimited | Teams wanting AI call transcription and summaries |
| GoTo Connect | Quote-based | Unlimited | Businesses with international calling to 50+ countries |
| Vonage | £10 | Unlimited | Sales teams needing supervisor tools (whisper/barge) |
| 8×8 | Quote-based | Unlimited | Contact centres with unlimited calls to 48 countries |
Every provider above includes unlimited simultaneous calls as standard – there is no per-line limit like traditional systems. Whether you have 5 or 500 users, each person can be on a call at the same time without any capacity constraints beyond your broadband bandwidth.
How Many Lines Does Your Business Need?
With cloud VoIP, you do not need to calculate “lines” – every user gets their own extension with unlimited simultaneous call capacity. The old concept of counting phone lines is 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 the system handles unlimited concurrent calls. The only 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-£50/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 as standard – 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 everything 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 (100-250 participants depending on provider)
- CRM integration – caller info from Salesforce, HubSpot, or Zoho pops up when the phone rings
- AI transcription – automatic call notes and summaries (Dialpad, RingCentral)
These features are not add-ons – they come with every plan from every major provider. The only variation is in limits (for example, video meeting participant caps) and which specific CRM integrations are supported.
How Much Does a Multi-Line Phone System Cost?
Cloud multi-line systems cost £7-£25 per user per month with no hardware investment. A 10-person office pays £70-£250/month all-inclusive, compared to £4,000-£8,000 upfront for equivalent traditional hardware.
| Cost Element | Cloud VoIP | Traditional Multi-Line PBX |
|---|---|---|
| Hardware | £0 (use existing devices) or £50-£150 per IP desk phone | £1,000-£10,000+ for the PBX unit |
| Monthly per user | £7-£25 | £15-£30 per ISDN channel + maintenance |
| Calls | Unlimited UK calls included | Per-minute billing on most tariffs |
| Installation | Self-setup, same day | £500-£2,000 (engineer required) |
| Adding users | Free – add online instantly | £50-£150 per additional extension (hardware) |
| Maintenance | Included | £50-£200/month contract or per-callout |
Example: 10-person business. A cloud multi-line system with bOnline costs £70/month (10 users x £7). With RingCentral including video conferencing and integrations, it is £130/month. An equivalent traditional PBX setup would cost £3,000-£6,000 upfront, plus £200-£400/month 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 annual billing savings of 15-25% compared to monthly payment.
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 the simplest and cheapest multi-line setup from £7/user. For businesses that need integrations, video conferencing, and advanced analytics, RingCentral (from £12.99/user) is the most complete platform. Teams with heavy international calling should look at GoTo Connect (free calls to 50+ countries) or 8×8 (48 countries).
If you are still using a traditional multi-line system connected to BT lines or ISDN, start your migration now. The process takes 1-2 weeks including number porting, 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.
