How Andisa IT moved a Harrogate business from an unreliable on-premise 3CX phone system to a managed, cloud-hosted 3CX platform without losing the ability to take customer calls.

Written by Andy Morrison, Managing Director, Andisa IT. Technically reviewed by Paolo Medori, 3CX Advanced Engineer. Published 21/10/26. Last updated 21/10/26.

IN BRIEF
Andisa IT migrated Cryonorm Process Combustion’s on-premise 3CX phone system to Andisa’s private cloud in 2023 without any loss of customer calls. We built and tested the new 3CX system in parallel with the old one, used a 3CX Session Border Controller to move phones in stages, and switched over only once users were ready. The platform has run without a fault since 2024.

PROJECT AT A GLANCE

DETAIL	SUMMARY
Client	Cryonorm Process Combustion Ltd, now Cryonorm, part of the Charter Industries group
Location	Harrogate, North Yorkshire
Sector	Industrial process combustion
Employees	Approximately 25
Project	3CX on-premise to cloud migration, call flow redesign and ongoing management
Completed	2023
Starting point	Self-designed, self-hosted system on an earlier version of 3CX, V16
Now running	3CX hosted in Andisa’s private cloud
Lost customer calls during migration	None
Key technology	3CX, 3CX Session Border Controller, 3CX softphone, 3CX mobile app, SIP trunk
Result	No faults since 2024, fewer missed calls, full support for mobile and hybrid working

The challenge: an unreliable on-premise 3CX phone system

Cryonorm Process Combustion Ltd is a Harrogate business with around 25 employees. It ran a self-designed telephone system built on an earlier version of 3CX and hosted on-premise. Over time, the system created three problems.

Reliability. The on-premise PBX went offline periodically.
Missed calls. The call routing created “black holes” where customer calls went unanswered, with no clear record of what had happened.
Voicemail. Messages sat in individual mailboxes and depended on each person remembering to check them, so an important customer message could go unheard.

The business also needed a phone system that worked away from the office. Staff used a mix of desk phones and softphones, and more of them were working remotely.

Our objective went beyond replacing the phone system. We wanted to redesign how calls were handled and give Cryonorm a reliable, managed communications platform that made it easier for customers to reach the right person.

Upgrade on-premise 3CX or migrate to the cloud?

Upgrading the existing on-premise installation would have left the same weaknesses in place: a system hosted on site, designed in-house and not monitored by a specialist. We recommended moving 3CX into Andisa’s private cloud instead.

Hosting 3CX in our managed infrastructure means we take responsibility for:

Monitoring and backups
3CX software upgrades
SIP trunk functionality
Adding and changing users
Future changes to call flows

How we migrated 3CX to the cloud without downtime

There was one hard constraint: Cryonorm could not lose its phones. Its customers need to reach it, so switching the old system off while we installed the new one was not an option. Instead of treating the migration as a single cutover, we ran it in six stages.

Designed a new 3CX environment. We built a fresh 3CX system for Cryonorm on Andisa’s private cloud infrastructure, designed around how the business actually handles calls.
Built it in parallel. The new system ran alongside the existing on-premise PBX, which stayed live and kept taking customer calls.
Tested with a trial licence and a test number. A 3CX trial licence and an additional telephone number let us configure and test the new environment with Cryonorm before any live calls moved.
Installed a 3CX Session Border Controller on site. The SBC connects the desk phones in the Harrogate office to the cloud-hosted 3CX system.
Moved phones in stages. Lower-use phones moved across in a few minutes each. The key phones handling most customer calls stayed on the old platform until the end, and we set up 3CX softphones in advance for the staff who answer the most calls.
Switched over once everything was proven. We moved the 3CX licence to the new environment and registered the replacement system with the SIP provider.

The result: Cryonorm moved to a cloud-hosted 3CX phone system without losing the ability to make or receive customer calls. Careful planning and testing meant the technology changed underneath the business without disrupting the people using it.

How long were the phones offline?

Customer calls were never interrupted. Individual lower-use handsets were unavailable for a few minutes each while they moved to the new system. The main call-handling phones stayed live on the old platform until the final switch, and the busiest users already had softphones ready.

What the 3CX Session Border Controller did

A 3CX SBC sits on the office network and relays traffic between on-site IP phones and a remote 3CX system. It meant we could move desk phones to the hosted platform one at a time, while the rest of the office carried on as normal.

Redesigning 3CX call flows to stop missed calls

Moving 3CX to the cloud fixed the reliability of the platform. We also wanted to improve what happens when a customer calls.

IVR routing. A new Interactive Voice Response (IVR) menu routes incoming calls quickly to the right department.
Overflow to a secondary team. If the primary team does not answer, the call passes automatically to a secondary team with the skills to help. An unanswered call no longer reaches a dead end.
Automatic call reports. 3CX call reports are emailed to the business, so management and staff can see missed calls and how well calls are handled against their service expectations.

Voicemail to email: making voicemail a team responsibility

Voicemail no longer goes to an individual phone account. Messages are delivered by email to a team mailbox, so colleagues can see when a message arrives and someone takes responsibility for replying. It is another way we closed the communications “black holes”.

Voicemail to email: making voicemail a team responsibility

3CX for mobile and hybrid working

The cloud-hosted 3CX platform gives Cryonorm’s staff far more flexibility. Employees use the 3CX mobile app on their phones when away from the office. PC and laptop users work with the 3CX softphone and a USB headset. The business phone system no longer depends on someone sitting next to a particular handset in the Harrogate office.

The results

No lost customer calls during the migration from on-premise to cloud-hosted 3CX.
No faults since 2024.
Every unanswered call has a next destination, through IVR and overflow routing.
Missed calls are visible to management through automatic emailed call reports.
Voicemail is shared by the team, not held in one person’s mailbox.
Staff take business calls anywhere, from the office, at home or on the road.
Updates install outside business hours, with no disruption to the working day.
Reduced missed calls from 98% to zero lost calls, with every call now either answered or a voicemail emailed directly to the Senior Admin for processing.
Eliminated black holes in the call flow, ensuring every incoming call has a clear outcome.

That reliability held while the organisation went through significant change. Cryonorm Process Combustion was formed from the merger of Process Combustion and Dutch company Cryonorm, and has since become Cryonorm, part of the Charter Industries group. The managed 3CX platform supported the business throughout.

Chaos-free IT is what we promise. This project shows what it means in practice: technology that is properly planned, proactively managed and quietly gets on with its job.

Planning your own 3CX upgrade or migration: lessons from this project

Whether you are planning a 3CX version upgrade, a move to a new server or a migration from on-premise to cloud, these principles kept Cryonorm’s phones working.

Build the new system alongside the old one. Do not switch off the live system until the replacement is proven.
Test away from live calls. A trial licence and a spare number let you test everything without touching production.
Move phones in order of call volume. Low-use handsets first, main call handlers last.
Prepare softphones and the mobile app in advance for your busiest users, so they have a fallback on switchover day.
Plan the licence transfer and SIP trunk registration as one scheduled step.
Back up the existing system and document current call flows before any change.
Fix call flows, do not just copy them. A migration is the best time to remove routing gaps.

More than a phone system

Andisa’s relationship with Cryonorm extends beyond 3CX. We also provide ongoing managed IT support, cyber security, backup services and leased-line connectivity. Bringing these together means Cryonorm’s IT and communications are managed as one technology strategy, not as isolated systems from different suppliers.

3CX upgrade and migration FAQs

Yes, with the right approach. For Cryonorm, we built the new 3CX system in parallel with the old one, tested it with a trial licence and a spare number, then moved phones in stages. Customer calls were never interrupted. The key is to keep the live system running until its replacement is proven.

With a parallel build, your main call handling does not need to go offline. During Cryonorm’s migration, lower-use handsets moved across in a few minutes each, and the phones taking most customer calls stayed live until the final switch. An in-place upgrade with no fallback system carries more risk if something goes wrong.

It depends on why you are upgrading. If your on-premise 3CX system is reliable and well maintained, an upgrade may be enough. If it goes offline, relies on one person’s knowledge or does not support remote working, a managed cloud-hosted 3CX platform removes those problems. Cryonorm moved to the cloud for all three reasons.

Cloud hosting suits most small and mid-sized businesses. It removes the risk of an on-site server, supports remote and mobile working, and lets a provider handle monitoring, backups and updates. On-premise hosting can suit organisations with specific control or compliance needs. Cryonorm’s cloud-hosted 3CX platform has run without a fault since 2024.

Build a new hosted 3CX environment and run it in parallel with the existing system. Test it using a trial licence and a separate number. Connect on-site desk phones through a 3CX Session Border Controller, move phones in stages, then transfer the licence and register the new system with your SIP provider. This is the process we followed for Cryonorm.

3CX supports backing up a system and restoring it to a new server or hosting environment, subject to version compatibility. For Cryonorm, we chose to design a new environment instead, because the old call routing was part of the problem. A migration is a good time to decide which settings are worth keeping.

A 3CX Session Border Controller (SBC) is a small software gateway installed on a site’s local network. It relays traffic between the office IP phones and a remote or cloud-hosted 3CX system. For Cryonorm, the SBC let us move desk phones to the new cloud system one at a time while the rest of the office carried on as normal.

Usually, but it needs planning. Your SIP provider must support the 3CX version you are moving to, and the new system must be registered with the provider. For Cryonorm, registering the replacement system with the SIP provider was part of the final, scheduled switchover. Check compatibility with your provider before you start.

They can be carried over or redesigned. For Cryonorm, we redesigned them: a new IVR routes callers to the right department, and overflow rules pass unanswered calls to a secondary team. A migration is the ideal time to fix the routing gaps that cause missed calls.

Andisa IT is a Harrogate-based managed IT provider that designs, migrates and manages 3CX business phone systems, including on-premise to cloud migrations like Cryonorm’s. We host 3CX in our private cloud and manage it alongside IT support, connectivity and cyber security for businesses across Yorkshire and the UK.

Cost depends on the number of users and handsets, your current 3CX version, whether you stay on-premise or move to the cloud, any SIP trunk changes and how much call flow redesign you need. For example, 3CX cloud migrations for a 25-user business typically start from £495.

Planning a 3CX upgrade or cloud migration?

Whether you need to upgrade an existing 3CX system, move 3CX to a new server or migrate from on-premise to the cloud, Andisa IT plans the work so your phones keep working. We design, migrate and manage 3CX business phone systems from our base in Harrogate, alongside IT support, connectivity and cyber security, for businesses across Yorkshire and the UK.

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