Last Tuesday, honestly, I thought we had this one wrapped. A 28-person manufacturing firm in Sheffield, 2 office sites, PRI circuits from 2011, mobile twinning that had never worked properly. The owner wanted off ISDN before the end of the quarter. From my experience, these migrations take about 2 weeks start to finish. We did this one in 48 hours and I will tell you everything that broke.
The starting state
| Item | Detail |
|---|---|
| Site A (head office) | ISDN30, 30 channels, 14 handsets |
| Site B (factory) | ISDN2e, 8 channels, 6 handsets |
| Current monthly | £1,847 (inc maintenance) |
| Router A | Cisco 887, no SIP ALG config |
| Router B | BT Business Hub (consumer kit) |
| Main pain point | No mobile app, no remote work support |
What went wrong (in order)
Hour 4: SIP ALG on the factory router
The factory had a BT Business Hub because nobody had bothered to upgrade it in 7 years. SIP ALG was on by default, and the hub had no way to switch it off through the GUI. Had to enable remote management on the router, SSH in, disable via CLI. 90 minutes.
If you are doing a migration and the customer has consumer-grade kit at any site, tbh just replace the router. A £180 MikroTik hAP ax² solves 80% of SIP issues before they happen. We learned this the hard way on 3 previous jobs.
Hour 11: The porting request failed
Submitted the number port at 09:40. Rejected at 15:20. Reason: account holder name on the BT account was "Sheffield Manufacturing Ltd" but the Companies House name was "Sheffield Manufacturing Limited". One word difference, port rejected.
We got it wrong for about 3 hours before we spotted it. Re-submitted with exact match, port scheduled for next morning.
Hour 19: Mobile app notification failures on 3 Samsung devices
Three of the factory foremen were on Samsung Galaxy A53s. App installed, logged in, but notifications just did not arrive for incoming calls. Battery optimisation was killing the app in the background. This is a known issue and it is embarrassing that we did not pre-brief the customer. Had to walk each foreman through Settings > Apps > DialPhone > Battery > Unrestricted.
Hour 36: The call quality complaint
Factory floor staff said calls sounded "tinny". Turned out the factory's industrial WiFi was on 2.4 GHz only, with 47 devices competing for 3 non-overlapping channels. Voice packets were losing to a PLC doing telemetry. Added QoS rules on the MikroTik, priority 7 for RTP traffic, problem gone in 20 minutes.
Final state
| Metric | Before | After 48h |
|---|---|---|
| Monthly cost | £1,847 | £672 (28 × £24) |
| Mobile app in use | 0 | 28/28 |
| Remote work enabled | No | Yes |
| Call recording | £180/mo add-on | Included |
| Videoconferencing | None | Included |
Lessons I am writing down for next time
- Consumer routers get replaced on day 1, not negotiated around
- Match the porting account name to Companies House, letter for letter
- Samsung battery optimisation checklist goes into the pre-call with every customer
- Industrial WiFi needs QoS from hour zero
48 hours is aggressive but doable if you have done it 200 times. Budget 2 weeks if it is your first. And if you are evaluating providers, ask them about the last migration they did that went sideways. Anyone who says "they all go smoothly" has done three of them.
DialPhone runs UK VoIP for small and medium businesses. We are happy to look at your existing invoice and tell you what the real migration risks are before you commit.