Managing phone systems across multiple UK locations used to require separate PBX boxes, separate contracts, and separate phone numbers at each site. In 2026, a single cloud VoIP system connects every office under one platform.
Here is how to do it properly — from a consultant who has connected 80+ multi-site UK businesses.
The Architecture
Cloud VoIP Platform (single system)
|
+--- London HQ (50 users)
| Extensions: 1000-1049
| Local number: 020 XXXX XXXX
|
+--- Manchester (25 users)
| Extensions: 2000-2024
| Local number: 0161 XXX XXXX
|
+--- Edinburgh (15 users)
| Extensions: 3000-3014
| Local number: 0131 XXX XXXX
|
+--- Birmingham (20 users)
Extensions: 4000-4019
Local number: 0121 XXX XXXX
Every office has local phone numbers. Every employee has the same extension regardless of location. Internal calls between offices are free and instant — dial the 4-digit extension.
What Multi-Site VoIP Solves
| Problem (Old Way) | Solution (Cloud VoIP) |
|---|---|
| Each office has separate phone system | One system, one admin portal |
| Inter-office calls cost money | Free — internal extensions |
| Cannot transfer calls between sites | Transfer to any extension, any site |
| Each office has separate auto-attendant | Unified IVR with site-specific routing |
| New office needs PBX installed | Add users in admin portal, ship phones |
| Reception cannot see who is free at other sites | Presence indicators across all sites |
The Setup Process for Each New Site
| Step | Time | What Happens |
|---|---|---|
| 1. Assign extensions | 5 min | Add users in admin portal |
| 2. Get local number | Instant | Choose 01/02 area code number |
| 3. Ship phones | Next day | Pre-configured, auto-provision on arrival |
| 4. Configure routing | 15 min | Ring groups, auto-attendant for new site |
| 5. Port existing numbers | 5-10 days | If keeping old numbers |
Total effort to add a new site: 30 minutes of admin time + wait for phones to arrive.
Compare to the old way: order PRI circuits (4-6 weeks), buy PBX hardware (procurement + delivery), hire installer (schedule + travel), configure (2-3 days on-site).
Network Requirements Per Site
| Site Size | Concurrent Calls | Bandwidth Needed | Recommended Connection |
|---|---|---|---|
| 5-10 users | 3-5 | 500 Kbps | Any broadband |
| 10-25 users | 8-12 | 1.2 Mbps | Business broadband |
| 25-50 users | 15-25 | 2.5 Mbps | Business fibre |
| 50-100 users | 30-50 | 5 Mbps | Dedicated fibre |
Critical at every site:
- QoS configured on the local router
- SIP ALG disabled
- Voice VLAN if possible (not mandatory for < 25 users)
Call Routing Strategies
Strategy 1: Follow-the-Sun
Calls route to the office that is currently in business hours:
- 8 AM - 5 PM UK: London/Manchester handle calls
- 5 PM - 8 PM UK: If you have a team in a later timezone, route there
- After hours: voicemail or on-call mobile
Strategy 2: Overflow Between Sites
If London reception is busy (all agents on calls), overflow to Manchester reception automatically. The caller does not know they are talking to a different office.
Strategy 3: Skills-Based Across Sites
Billing queries go to the billing team — regardless of which office they sit in. A billing-trained agent in Edinburgh takes the call if London billing is busy.
Common Multi-Site Mistakes
| Mistake | Impact | Fix |
|---|---|---|
| Different VoIP providers per site | Cannot transfer between sites | Use one provider for all sites |
| No QoS at remote sites | Poor quality at smaller offices | Configure QoS everywhere |
| No backup internet at critical sites | Office goes dark if ISP fails | Dual ISP or 4G backup |
| Extension numbering conflicts | Extension 100 exists at 3 sites | Use site-prefix numbering (1xxx, 2xxx) |
Cost Comparison
| Approach | 4-Site Monthly Cost | Setup Cost |
|---|---|---|
| Separate PBX per site | £6,800 | £45,000 |
| Hosted PBX (separate instances) | £3,400 | £5,000 |
| Unified cloud VoIP | £2,640 | £0 |
Unified cloud VoIP is 61% cheaper than separate PBXes and requires zero upfront investment.
DialPhone specialises in multi-site UK deployments. One system, one bill, one support team across all your locations. Each site gets a local number, instant inter-site calling, and unified management from a single admin portal.
