For many organisations, the decision to delay replacing legacy phone systems feels like a sensible one.
Budgets are tight. The current system “still works”. And a full PBX replacement can feel like a disruptive, time-consuming project that’s easy to push into the next financial year.
But across the public sector and enterprise environments we work with, we’re seeing a different reality emerging.
The true cost of holding onto legacy telephony isn’t static, it’s increasing. Quietly, but consistently.
And for many organisations, the tipping point is arriving faster than expected.
Why organisations are delaying replacement
Let’s start with the obvious question: why hasn’t everyone already moved on?
From our experience working with councils, housing associations, universities and NHS organisations, the reasons are consistent:
- “It still works, so why change it?”
- Concerns around migration complexity
- Fear of disruption to critical services
- Existing investment in platforms like Mitel, Avaya or Cisco
- Budget constraints and competing priorities
There’s also a perception that modernisation means a full “rip and replace” which understandably puts people off.
In reality, most organisations are not avoiding change altogether they’re simply delaying it.
And that delay is where the hidden costs begin to build.
Rising support and maintenance costs
Legacy PBX systems don’t get cheaper to run over time
As platforms age:
- Support contracts become more expensive
- Spare parts become harder to source
- Vendor support reduces or disappears completely
- Maintenance moves from proactive to reactive
We’ve worked with organisations maintaining legacy estates across Mitel, Unify, Cisco and Avaya where support has shifted into short-term, break-fix models just to keep systems operational.
This is fine as a short-term strategy, but it’s not a long term, sustainable plan
At some point, you’re no longer investing in your communications platform… you’re simply keeping it alive.
Security and resilience concerns
Legacy systems weren’t designed for today’s world.
Modern communications environments need to support:
- Remote and hybrid working
- Integration with collaboration tools like Microsoft Teams
- Multi-channel contact (voice, chat, email, social)
- Real-time reporting and analytics
Older PBX platforms struggle to meet these requirements without complex workarounds.
There are also increasing risks around:
- Security vulnerabilities on unsupported platforms
- Lack of patches or updates
- Limited disaster recovery options
- Single points of failure
In contrast, cloud and hybrid solutions are designed with resilience and scalability built in, often with significantly higher uptime and redundancy.
Skills shortages for legacy platforms
One of the least talked-about challenges is people.
The engineers who specialise in legacy telephony platforms are becoming harder to find – we’ve been doing this for nearly 40 years and the skills gap is definitely growing
Many have moved into cloud, Teams Voice, or contact centre technologies and fewer new engineers are being trained on older systems.
That creates a very real operational risk:
- Longer resolution times
- Increased reliance on a shrinking pool of specialists
- Higher support costs
- Greater exposure during outages
This is particularly important for organisations where service continuity is critical.
When migration becomes unavoidable
Most organisations don’t move because they want to.
They move because they have to.
Typically, that trigger comes in one of the following scenarios:
- Hardware failure with no immediate replacement
- End-of-life or end-of-support announcements
- Contract renewals that no longer make financial sense
- Business requirements that legacy systems simply can’t support
The challenge is that at this point, the organisation is often reacting, not planning.
And reactive migrations tend to be:
- More expensive
- More disruptive
- More constrained in terms of options
The safest, most cost-effective path is to move before you’re forced to.
Creating a phased migration roadmap
The good news is that telephony modernisation doesn’t need to be a big bang project.
In fact, the most successful Teams Voice migration and Mitel migration projects we’ve delivered follow a phased approach.
This typically includes:
- Stabilise the existing estate
Maintain and support the legacy PBX where needed, reducing immediate risk.
- Introduce a hybrid model
Integrate Microsoft Teams with the existing platform allowing both systems to coexist.
This allows you to:
- Retain existing number ranges
- Move users in phases
- Avoid disruption to business-critical services
(We’ve seen this approach used effectively across councils and universities to support gradual migration at scale.)
- Migrate users based on business need
Move departments or user groups to Teams Voice as requirements evolve.
- Extend functionality
Introduce contact centre capabilities, AI routing, analytics and reporting within Teams.
- Decommission legacy systems
Once usage has reduced sufficiently, retire the PBX without risk.
This approach turns what feels like a large capital project into a controlled operational programme.
Final thoughts: cost vs risk vs timing
The decision to delay PBX replacement often starts as a financial one.
But over time, it becomes a risk decision.
And then, it becomes a timing decision, usually not on your terms.
Legacy phone systems don’t fail overnight.
But the combination of rising costs, reduced support, increasing risk and limited flexibility means that the longer they remain in place, the harder and more expensive the transition becomes.
The organisations seeing the best outcomes aren’t necessarily the ones moving fastest.
They’re the ones planning earliest.
If you’re reviewing your telephony strategy
Whether you’re considering a full PBX replacement, exploring Teams Voice migration, or planning a phased Mitel migration, the important step is to understand your options early.
A short discovery session can often highlight:
- Cost savings opportunities
- Migration approaches
- Risk areas in your current estate
- A realistic roadmap aligned to your organisation