The retirement of Australia's legacy voice infrastructure has been running for years, and it’s now in its final phase for business services. If your business still has ISDN 10/20/30 services, ISDN BRI lines, or copper PSTN lines feeding an on-premise PBX, you’re on borrowed time and the last businesses to move will be the ones paying premium rates for rushed migrations.
This guide is written for the business owner or office manager who has received a letter from their carrier and isn’t entirely sure what it means.
1. What Is Actually Being Switched Off
Three separate things get conflated in these announcements:
- The PSTN (Public Switched Telephone Network). The copper-based analogue phone network. Most premises have already migrated as part of the NBN rollout, with copper voice services disconnected in NBN-ready areas.
- ISDN (Integrated Services Digital Network). The digital service that has carried multi-line business phone systems since the 1990s. ISDN BRI and PRI services are being progressively decommissioned nationally.
- Legacy hosted products, older carrier-managed phone products built on that infrastructure are also being retired and replaced with cloud offerings, sometimes at higher prices.
What replaces them is IP-based: SIP trunking into an existing PBX, or a fully hosted cloud PBX with no on-premise hardware at all. Exact disconnection dates vary by service, carrier, and location, so the only authoritative source is your own carrier: call them and ask for the disconnection date for each service ID on your account, in writing.
2. Are You Affected? A Quick Test
You’re likely affected if any of the following are true:
- There’s a phone system cabinet in your comms room with cards or modules in it
- Your phone bill lists "ISDN", "BRI", "PRI", "OnRamp", "InDial", or a block of DID numbers
- Your handsets are wired to a punch-down block rather than to your data network switches
- You pay a monthly line rental per phone line, separate from your internet service
- You’ve an annual maintenance contract with a phone system technician
If you’re unsure, the fastest check is your most recent invoice. Legacy services are itemised as line rentals; IP services are itemised as channels, seats, or users.
3. The Hidden Devices Everyone Forgets
This is where migrations go wrong. Voice lines in Australian businesses carry far more than voice, and each of these devices needs its own plan.
| Device on a Legacy Line | Risk if Missed | Replacement Approach |
|---|---|---|
| Back-to-base alarm dialler | Monitoring silently fails; insurance implications | IP or 4G alarm communicator, tested with the monitoring centre |
| Lift emergency phone | Regulatory and safety exposure | 4G lift dialler; coordinate with your lift contractor |
| EFTPOS terminal | Payments fail at the counter | IP or mobile-network terminal from your bank |
| Fax machine | Inbound faxes silently lost | Fax-to-email service on the same number |
| Fire panel dialler | Compliance breach | Certified IP/4G path via your fire services contractor |
| Gate and intercom systems | Site access failure | SIP-capable intercom or 4G module |
| Modem for remote plant/telemetry | Loss of monitoring on equipment | 4G router or IP telemetry |
Walk the building. Physically trace every phone socket and note what is plugged into it. In our experience, the average small office finds two devices nobody remembered and one nobody could identify.
4. Your Replacement Options
Option A: SIP trunks into your existing PBX
If your on-premise PBX is IP-capable and less than about six years old, SIP trunking replaces the ISDN service while keeping your hardware and handsets. It’s the smallest change and the cheapest immediate step.
Suits: businesses with a recent, functioning PBX and a large investment in handsets.
Against: you still own and maintain hardware, you still pay for maintenance contracts, and you’ll face the same decision again when that PBX reaches end of life.
Option B: Hosted cloud PBX
Retire the on-premise system entirely. Users get desktop and mobile apps plus optional desk phones; the call handling logic lives in the provider's platform. This is the destination the market has settled on, and for most Australian businesses under 200 staff it’s both cheaper and more capable.
Suits: almost everyone, particularly businesses with remote staff, multiple sites, or an ageing PBX.
Against: requires a reliable internet connection with sensible quality-of-service configuration.
Option C: Carrier's own replacement product
Your existing carrier will offer a migration path onto their cloud product. It’s convenient, and it’s very often the most expensive option on a per-user basis. Get at least two competing quotes before accepting the default upgrade, our 2026 pricing guide shows the spread.
Don’t treat this as a like-for-like swap
The businesses that get the most out of the shutdown are the ones that treat it as a chance to redesign. You’re already replacing the system: this is the moment to add mobile apps, call recording, CRM integration, and AI call handling, not to recreate a 1998 call flow on new infrastructure.
5. The Migration Checklist
- Inventory every service. List every phone number, line, and channel on your bill, plus what each one is used for.
- Inventory every device. Use the table in section 3 as your starting point and walk the site.
- Map your call flows. Who answers what, in which order, at what times, and where calls overflow.
- Check your internet. Estimate roughly 100 kbps per concurrent call in each direction and confirm your connection and router can prioritise voice traffic. See our NBN call quality guide.
- Choose your replacement. Shortlist three providers, compare on total monthly cost including calls.
- Lodge the port request early. Complex ports of number ranges take substantially longer than single numbers, see our porting guide.
- Pre-configure and test. Build the new call flows before cutover and test every path, including after-hours and holiday routing.
- Run parallel where possible. Keep the old service live for a short overlap so you can fall back.
- Verify the non-voice devices. Test the alarm, the lift phone, the EFTPOS terminal, and the fire panel after cutover, with their respective monitoring providers on the phone.
- Cancel the old services in writing. Don’t assume they stop billing automatically.
6. A Realistic Timeline
| Business Size | Audit & Selection | Porting & Build | Cutover & Bedding In | Total |
|---|---|---|---|---|
| 1–10 users, few numbers | 1 week | 1–2 weeks | 1 week | 3–4 weeks |
| 10–50 users, DID range | 2 weeks | 3–4 weeks | 2 weeks | 7–8 weeks |
| 50+ users, multi-site | 3–4 weeks | 4–8 weeks | 2–4 weeks | 3–4 months |
Add contingency if you’ve critical non-voice devices, if your numbers are spread across multiple carriers, or if you’re also changing internet providers at the same time (which we would generally advise against doing simultaneously).
7. Risks of Leaving It Late
- Forced disconnection. When the date arrives, the service stops. There’s no grace period that depends on your readiness.
- Emergency pricing. Rushed migrations attract expedite fees, after-hours technician rates, and whatever hardware is in stock rather than what you actually wanted.
- Port queues. Everyone in your position is porting at the same time. Lead times lengthen as deadlines approach.
- Losing numbers. A number that’s disconnected before it’s ported can be very difficult, sometimes impossible, to recover. Port first, disconnect second: never the reverse.
- Untested safety systems. The worst outcome is discovering the lift phone or alarm dialler was on the old line at the moment you needed it.
8. Recommended Path
For the vast majority of Australian businesses coming off ISDN or PSTN, a hosted cloud PBX is the right destination. Not a SIP trunk into hardware that will need replacing again in a few years.
Uniden Voice over Cloud is our top-rated option for this migration for four practical reasons:
- Free number porting and free setup, which removes the largest one-off cost of the migration
- Australian-built and hosted, with local support staff who can be on the phone during cutover
- 40+ features included, so you can rebuild your call flows properly instead of replicating legacy limitations
- Mobile app failover, which means an internet outage no longer takes your phones down: something ISDN users often (rightly) worry about
Whichever provider you choose, start the audit this month. The audit is the part that takes the longest and the part nobody can do for you at the last minute.