Migration Guide

ISDN to VoIP Migration Guide — Australia

ConnectCX Advisory TeamPublished 10 March 2026· Updated 14 April 2026

With ISDN services being progressively disconnected across Australia, migrating to VoIP is no longer optional — it's essential. This guide covers your options, from SIP trunking to full cloud UCaaS.

Typical timeline: 2–6 weeks for most businesses. Complex multi-site migrations may take longer.

Step-by-step process

Understand your ISDN setup

Document your ISDN lines (BRI/PRI), connected equipment, phone numbers, and monthly costs. This is your migration baseline.

Check your internet

VoIP requires reliable broadband. Check your NBN speed and consider a dedicated voice VLAN or business-grade connection for quality assurance.

Choose your path

Option A: SIP trunking (keep your PBX, replace ISDN lines with SIP). Option B: Full cloud UCaaS (replace everything with a cloud platform). Option B is recommended for most businesses.

Select a provider

Compare providers that support Australian number porting and have local data centres. Use our free assessment for a recommendation.

Port your numbers

Initiate number porting from your ISDN provider. Keep ISDN active until porting completes (5–10 business days).

Deploy and test

Set up your new VoIP system, test all call scenarios, train staff, and go live. Cancel ISDN lines once confirmed working.

Benefits

Save 40–60% on phone bills vs ISDN line rental
Future-proof — ISDN is being switched off regardless
Add video calling, messaging, and AI features
Work from anywhere with softphones and mobile apps
Easier to manage and scale

Watch out for

NBN congestion during peak hours — consider a dedicated internet connection for voice
Power outages affect VoIP (unlike ISDN) — have mobile failover or a UPS
Fax machines may need special handling — use cloud fax services
Some legacy equipment may not be SIP-compatible

Frequently asked questions

When will my ISDN be disconnected?

Telstra and NBN Co are progressively disconnecting ISDN. Most areas will lose service by 2027, but some have already been affected. Check with your provider for your specific timeline.

What about fax machines?

Traditional fax machines don't work over VoIP reliably. Use cloud fax services (email-to-fax) which are included with most UCaaS providers.

Will VoIP work on NBN?

Yes. VoIP works well on NBN connections with adequate bandwidth. A typical call needs 100kbps. Business NBN plans with static IPs are recommended.

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