VoIP • Migration

VoIP migration checklist: 10 questions before you leave your old PBX

Moving off a legacy PBX is an infrastructure project, not just an upgrade. Get clear, written answers to these ten questions before you sign, and the switch is smooth instead of silent.

Last verified 9 June 2026
By the WhichVoIP editorial team
8 min read

10 questionsto ask before you sign

Port firstthen cancel, for zero silence

GNPkeeps your existing number

UPS + appkeeps calls up in an outage

The short answer

How do I migrate from an old PBX to VoIP without downtime?

Plan it as an infrastructure move. Confirm number porting, test that your internet is call-ready, and pin down costs, hardware, security and support in writing before you sign. The golden rule: port your number to the new system before you cancel the old line, so the business is never left in silence.

critical questions to ask

internet quality factors that matter

encryption layers to insist on

days of silence if you port first

An Old Pbx Box Being Replaced In A South African Office During A Voip Migration — The fear is never the technology; it is the process. A clear checklist turns the switch from a leap into a sequence.

Why SA businesses are leaving the old PBX behind

For decades a legacy Telkom or copper PBX was the backbone of business calling. In 2026 that ageing infrastructure is a liability, not an asset.

Ageing copper, expensive line rentals and hardware that cannot support remote work have made the move to VoIP a matter of when, not if. The anxiety is rarely about VoIP itself; it is about unplugging the old without dropping into communication silence. That is exactly what a disciplined migration prevents, and it starts with asking the right questions up front.

The 10 questions to get answered in writing

Before you sign a contract or book an installation, get clear written answers to all ten. This is your blueprint for a switch with no surprises.

Can I keep my existing business number?Your number is your identity. The process is Geographic Number Porting (GNP). Confirm the provider has a proven porting process, and ask about lead time and the documents required.

Is my internet truly VoIP-ready?VoIP runs on data, so the connection is the foundation. It is not just bandwidth: latency and jitter decide call quality. Ask for a network assessment that tests your line against your expected call volume.

What is the power and failover plan?VoIP needs power and internet. Ask the provider to recommend a UPS for your router, switch and key phones, and confirm the system includes a mobile app that takes over calls when the office is offline.

What are the real monthly costs in rands?Get a detailed quote. Does the price include numbers, hosting, support and a bundle of minutes? Are there separate per-user fees? Be clear on what is included versus a chargeable extra.

What new hardware do I actually need?Will you need all-new IP phones, or can existing gear work with an adapter? A modern setup includes softphone and mobile apps, so you may not need a desk phone for every person.

How secure is the platform?Ask specifically about call encryption (TLS and SRTP) and toll-fraud protection, where hackers hijack your system to run up huge international bills. Security should be a standard answer, not an upsell.

Which advanced features are included as standard?Do not assume an auto-attendant (IVR), call recording or reporting are included. Get the list in writing. This is where VoIP earns its keep over a legacy PBX.

What do onboarding and support look like?On-site or remote setup? What are the support hours and the guaranteed response time (SLA)? Local South African support that understands your context is a real advantage.

How easily does it scale up or down?If you hire three people, how fast can they be added? Can you scale down without penalty? The system should adapt to your business, not the other way round.

Can we have a live demonstration?Never buy a phone system unseen. Ask for a live demo on your use cases: transferring a call, setting up a conference, checking voicemail. A pre-recorded video is not enough.

✓

Bottom line: the single most important sequencing rule is to port your number onto the new system before you cancel the old line. Do that and the business never goes silent during the switch.

Legacy PBX versus modern VoIP, at a glance

The core differences you will be navigating, so you know what you are trading up from.

Challenge area	Modern VoIP	Legacy copper PBX
Cost structure	Low upfront, predictable per-user fee, cheaper calls, often free inter-branch	High upfront hardware, line rentals, costly call-outs
Scalability	Add or remove users in minutes via a web portal	New hardware cards and physical installs
Remote work	Use your extension anywhere via desk phone, softphone or mobile	Tied to the physical office
Power and failover	Needs power, but calls fail over to the mobile app	The PBX itself needs power, with no failover

The anxiety is never about VoIP. It is about how you unplug the old without plunging the business into silence.

WhichVoIP editorial view

A Tidy Modern Voip Desk Phone And Laptop Softphone Replacing An Old Pbx In A South African Office — The destination: one number reachable on a desk phone, a laptop softphone and a mobile, with the old copper line retired.

Our verdict

A VoIP migration goes wrong when a business treats it as a quick swap and skips the questions. It goes smoothly when you confirm porting, prove the internet is ready, plan for power and failover, and get costs, security and support in writing first. None of that is hard; it just has to happen before the installation date, not after.

Our recommendation: take these ten questions to every provider you shortlist and insist on written answers. Then port before you cancel, and keep a UPS on the router so a power dip never becomes a dropped call.

Ready to plan your switch?

Compare South African VoIP providers and get matched to ones that can answer all ten questions, with a quote tailored to your migration.

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Frequently asked questions

Can I keep my number when I move to VoIP?

Yes, through Geographic Number Porting (GNP). Confirm your chosen provider has a proven porting process, ask about the lead time, and have your documentation ready. Crucially, port the number onto the new system before you cancel the old line so you are never without it.

How do I avoid downtime during a VoIP migration?

Sequence it: get the internet tested and the new system ready, port your number across, confirm calls are flowing, and only then cancel the old line. Running both briefly in parallel means the business never goes silent.

Is my internet good enough for VoIP?

Maybe, but speed alone does not decide it. Latency and jitter matter as much as bandwidth. Ask any provider for a network assessment that tests your line against your expected call volume before you commit.

What happens to my calls during a power outage?

VoIP needs power and internet, so plan for both. A UPS keeps your router, switch and key phones running through short outages, and a good provider’s mobile app lets calls fail over to staff phones when the office is offline.

Will I need to buy all new phones?

Not necessarily. Some existing handsets work with an adapter, and modern VoIP includes softphone and mobile apps, so you may not need a desk phone for everyone. Ask the provider what your current hardware can and cannot do.

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Sources: WhichVoIP migration practice; standard SA number-porting (GNP) and VoIP-readiness guidance; TLS/SRTP encryption standards. Verified 9 June 2026.