On 30 September 2019, Telstra began decommissioning its ISDN services network. In 2020, NBN Co completed the National Broadband Network rollout across Australia. Together, these milestones marked the end of decades-old telephony technology — and made the transition to Voice over IP (VoIP) unavoidable for every Australian business still on ISDN.
What is ISDN?
ISDN stands for Integrated Services Digital Network. For decades it served as the backbone for business voice and data communications over copper telephone lines. The technology gained popularity because it delivered guaranteed bandwidth and supported multiple simultaneous services — voice and data — over standard copper cabling.
ISDN lines came in two common flavours: BRI (Basic Rate Interface) for smaller businesses, and PRI (Primary Rate Interface) for larger organisations needing more concurrent call capacity. Before VoIP, a PRI was how most medium-to-large businesses handled their phone systems.
What is VoIP?
Voice over IP (VoIP) sends and receives telephone calls over the internet using standard phone numbers. With a VoIP business phone system you can do everything you can normally do with a traditional phone system — plus a whole lot more.
VoIP operates as a subscription service delivered via your internet connection. There's no dedicated copper phone line required. Your existing NBN, fibre, or other broadband connection carries the voice traffic alongside your regular internet usage.
What does this mean for your business?
If your business was still using ISDN, the decision has already been made for you — the network is being switched off, area by area, as the NBN rollout progresses. Once NBN Co has completed the rollout in your area, you typically have 18 to 36 months to complete your migration before the phone service is terminated.
Don't leave it to the last minute. The biggest risk isn't the technology switch itself — it's number porting.
Plan ahead: porting takes time
Transferring business phone numbers from ISDN to VoIP (known as a CAT-C port) requires 8 to 12 weeks. This is not something you can rush. If you miss the disconnection deadline and your service is terminated before the port is complete, you risk losing your numbers entirely — numbers your customers have been calling for years.
The process requires paperwork, coordination with Telstra as the losing carrier, and careful scheduling. Caznet manages this process for you, but lead time is essential.
Caznet's solution
Caznet offers a Cloud Hosted PBX and VoIP service as a direct ISDN replacement. The system works over any internet connection regardless of provider, supports all standard phone features, and typically reduces monthly telephony costs significantly compared with ISDN rental agreements.
Your existing phone numbers are retained. Your staff keep the same handsets or can upgrade. The system is hosted in the cloud, so there's no on-premises PBX hardware to maintain.
If you're still on ISDN, or you're not sure — call us. We'll check your address, confirm your NBN status, and walk you through what the transition looks like for your business.