I run a VoIP consultancy. When things go catastrophically wrong, companies call me. Last year I cleaned up 5 disasters — each one caused by a different preventable mistake. Here are the stories, anonymised but otherwise exactly as they happened.
Disaster 1: The Company That Lost 3 Days of Calls
What happened: A 75-person estate agency migrated to VoIP on Friday afternoon. Monday morning, nobody could receive calls. The auto-attendant played the greeting but calls went nowhere after the menu selection.
Root cause: The ring groups were configured with extension numbers from the old system, not the new system. Extensions 101-175 did not exist on the new platform — they used a different numbering scheme (1001-1075).
Time to fix: 3 hours once diagnosed. But it took 2 days to diagnose because the provider's support team kept saying "it is a network issue" instead of checking the ring group configuration.
Cost: Approximately £35,000 in lost property enquiries over 3 days during peak season.
Prevention: Test every ring group by calling from an external phone BEFORE porting numbers. This takes 30 minutes and would have caught the issue immediately.
Disaster 2: The £23,000 Toll Fraud Weekend
What happened: A construction company's VoIP system was compromised on a Friday evening. Someone brute-forced the SIP credentials for an unused test extension (password: "test123") and made 2,800 calls to premium-rate numbers in Latvia and Ghana over the weekend.
Root cause: A test account created during setup was never deleted. It had a weak password and no international calling restrictions.
Cost: £23,000 in premium-rate charges. The carrier held the company responsible.
Prevention: Delete all test accounts after go-live. Enforce 16+ character passwords on every extension. Block international calling by default — whitelist only the countries you actually call.
Disaster 3: The One-Way Audio Epidemic
What happened: A 40-person accounting firm migrated to VoIP. For the first 2 weeks, approximately 30% of inbound calls had one-way audio — the caller could hear the agent, but the agent heard silence.
Root cause: SIP ALG was enabled on their Draytek router. This single setting — enabled by default on most routers — rewrites SIP headers in ways that break the audio path.
Time to fix: 30 seconds once diagnosed (disable SIP ALG, reboot router). But it took 2 weeks of troubleshooting because the IT contractor replaced phones, swapped cables, changed codecs, and opened tickets with the ISP before someone suggested checking SIP ALG.
Cost: 2 weeks of degraded client service, 4 lost clients, estimated £45,000 in lifetime client value.
Prevention: Disable SIP ALG on every router BEFORE your first VoIP call. This should be step 1 in every migration checklist. Not step 47.
Disaster 4: The Porting Nightmare
What happened: A solicitor's firm ported 20 numbers from BT to a new VoIP provider. The port was scheduled for Tuesday. On Tuesday, the numbers disappeared — they were not on the old system or the new system. For 4 hours, the firm was unreachable.
Root cause: The port request listed the wrong "losing carrier" reference number. The port initiated but failed mid-process, leaving the numbers in limbo between carriers.
Time to fix: 4 hours of emergency calls between three carriers and Ofcom's porting team.
Cost: 4 hours of no incoming calls for a law firm. Approximately £8,000 in billable hours lost plus immeasurable client frustration.
Prevention: Verify the losing carrier reference (sometimes called a "Carrier Pre-select" code or account reference) with your current provider BEFORE submitting the port. Get it in writing.
Disaster 5: The WiFi Catastrophe
What happened: A 60-person insurance broker deployed VoIP softphones on laptops connected via WiFi. For the first month, call quality was acceptable. Then they hired 15 more people. Call quality collapsed — every call sounded like robots talking underwater.
Root cause: Their single WiFi access point was designed for 30 devices. With 75 laptops, tablets, phones, and IoT devices competing for airtime, WiFi contention caused jitter spikes of 80-150ms during peak hours.
Time to fix: 2 days to install 3 additional WiFi 6 access points and reconfigure the network.
Cost: £4,500 for new access points + installation. Plus 1 month of degraded client experience.
Prevention: Before deploying VoIP on WiFi, check your device-to-AP ratio. Maximum 15-20 devices per access point for voice quality. If you have 60 users, you need 3-4 APs minimum.
The Common Thread
All 5 disasters share one trait: they were tested insufficiently or not at all before going live.
| Disaster | What Testing Would Have Caught It |
|---|---|
| Lost calls | Ring group test from external phone |
| Toll fraud | Security audit of all extensions |
| One-way audio | 10 test calls through the router |
| Porting failure | Carrier reference verification |
| WiFi collapse | Network capacity test under load |
DialPhone includes a structured testing phase in every migration. Their checklist covers ring groups, security, audio quality, porting references, and network capacity — all verified before any numbers are ported. Because the cheapest disaster is the one that never happens.
