Key Takeaways
- Australia's legacy copper phone network (PSTN) and business ISDN services are being decommissioned in phases through 2026 — if you're still on them, you have a real deadline.
- When the old line is switched off, an un-migrated business simply loses its phones. Waiting until the line goes dead is the one option to avoid.
- In almost all cases you can keep your existing phone numbers by porting them to an internet-based (VoIP) service.
- Modern phone services run over your internet connection, so plan for redundancy — a broadband outage shouldn't take your phones down with it.
For decades, business phones "just worked" over the copper network — a dedicated line that kept dialling even when the power or the internet went out. That era is ending. Australia's legacy PSTN (the traditional copper phone network) and ISDN (the digital business lines many multi-line offices still run on) are being retired, and the switch-off is happening on a schedule, not someday.
If your business still relies on ISDN or old copper lines, this isn't a "nice to plan for eventually" project. It's a deadline with a hard edge: once your service is disconnected, those phones stop — so the goal is to migrate calmly and keep your numbers, well before the cut-off.
What's Actually Being Switched Off
Two related things are ending:
- The copper PSTN — the standard "landline" most small businesses grew up with — has been progressively decommissioned as part of the NBN rollout across the country.
- ISDN services — the higher-capacity digital lines used by offices with multiple simultaneous calls, phone systems, or PABX hardware — are being disconnected in phases, with the process continuing through 2026.
The exact timing depends on your location, your carrier, and how your premises is connected. Some businesses were quietly moved across during the NBN transition without noticing; others — especially those with older on-site phone systems or ISDN — still need to act.
Why "Wait and See" Is the Wrong Move
The risk with legacy shutdowns is simple: if you do nothing, your phones eventually go silent. When the line is disconnected on its scheduled date, an un-migrated business can lose inbound and outbound calling with little warning — no orders, no enquiries, no way for customers to reach you.
Migrating ahead of time removes that cliff edge entirely. Done properly, the change is seamless: your numbers keep working, your team keeps taking calls, and the old line is retired in the background.
The Good News: You Can Keep Your Numbers
One of the biggest fears business owners have is losing a phone number they've advertised for years. In almost all cases, you don't have to. Your existing local numbers — and inbound numbers like 1300 and 1800 — can generally be ported across to an internet-based service, so customers dial the same number and reach you exactly as before.
Porting is a routine part of a well-planned migration. The key is to start early enough that numbers are transferred before the legacy line is disconnected, not after.
What You're Moving To
The modern replacement for copper and ISDN is internet-based calling — VoIP, delivered over your NBN or business internet connection. For most businesses that means one of:
- A hosted phone system — your phone system lives in the cloud, and your team takes calls on desk phones, a desktop app, or their mobiles.
- SIP trunking — if you have a capable on-site phone system you want to keep, SIP trunking replaces your ISDN lines with internet-based channels, often without replacing your handsets.
Both approaches scale up and down far more easily than fixed copper or ISDN lines, and they add features — call routing, presence, remote working — that legacy lines never offered. (If you're weighing the two, our guides on VoIP vs traditional phone systems and what SIP trunking is go deeper.)
The One Trade-Off to Plan For: Internet Dependency
Here's the honest catch. Old copper lines had their own power and kept working in a blackout. Internet-based phones don't: if your internet goes down, your phones go down too — unless you've planned for it.
This isn't a reason to avoid migrating (you don't have a choice on that), but it is a reason to migrate thoughtfully. Sensible redundancy options include:
- Mobile failover / softphone apps so calls can still be answered on staff mobiles when the office connection drops.
- Automatic call redirection rules that send calls to another number or voicemail-to-email if your main service is unreachable.
- A backup internet path (for example a mobile broadband failover) for business-critical sites.
A good provider builds this resilience into the design rather than leaving it as an afterthought.
Your Migration Checklist
- Confirm what you're on. Are you still using ISDN, a PABX with legacy lines, or old copper phone lines? If you're unsure, that alone is worth a conversation.
- Find your disconnection date. Migration should be finished before it, with a buffer for number porting.
- List your numbers. Every local, 1300 and 1800 number you want to keep — so nothing gets missed in the port.
- Choose your replacement. Hosted phone system, SIP trunking, or a mix, based on your existing equipment and how your team works.
- Design for outages. Decide how calls keep flowing if the internet drops.
- Port, test, and cut over before the old line is switched off.
The legacy shutdown is one of those rare deadlines that turns a "we should probably upgrade" into "we need to move." The businesses that handle it well don't just avoid losing their phones — they come out the other side with a more flexible, feature-rich system than copper ever gave them.
Not sure where your business stands, or when your line is due to be switched off? Get in touch and we'll help you map out a migration that keeps your numbers and your calls running.
