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With Telstra's ISDN network fully decommissioned since mid-2022 and the NBN rollout pushing businesses toward IP-based connectivity, SIP trunking has become the default voice infrastructure for Australian organisations.
SIP trunking uses the Session Initiation Protocol (SIP) to deliver voice, video, and messaging over an internet connection instead of traditional phone lines. Rather than relying on physical copper circuits, a SIP trunk creates a virtual connection between your phone system (PBX) and the public switched telephone network (PSTN). This means your existing PBX can make and receive calls over your data network, eliminating the need for dedicated ISDN or analogue lines.
For a deeper technical overview, see What is SIP trunking? on the Telnyx resource hub.
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Three forces are accelerating SIP adoption across Australia.
The ISDN shutdown is complete. Telstra issued a cease‑sale on all ISDN products in June 2018 and began disconnections in September 2019, with a final exit date of 31 May 2022 for ISDN 10/20/30 services. Businesses that relied on ISDN for decades had no choice but to migrate. Those that delayed risked losing their phone numbers and experiencing service outages.
The NBN rollout reshaped connectivity. As the National Broadband Network replaced copper infrastructure across the country, existing landline and ADSL services were progressively disconnected. The NBN's Traffic Class 1 (TC1) product was designed to support VoIP, giving businesses a clear path from analogue voice to internet‑based telephony with QoS.
Cost pressure is real. The global SIP trunking market was valued at roughly USD 14 billion in 2024, with estimates projecting USD 30–37 billion by 2032 (10–13% CAGR) (Zion Market Research, Data Bridge Market Research). Organisations are moving to SIP because it delivers measurable savings compared to legacy telephony. Industry analyses consistently show that businesses migrating from PRI or ISDN to SIP trunking reduce monthly voice costs by 30–60%.
Deploying SIP trunking in Australia involves specific considerations around compliance, number portability, and number types.
ACMA compliance. The Australian Communications and Media Authority (ACMA) regulates telecommunications numbering, including rules around number allocation, portability, and service standards. Providers must comply with the Telecommunications Numbering Plan 2025 and relevant industry codes, and meet obligations for emergency calling (Triple Zero) and the Integrated Public Number Database (IPND).
Number portability. Australian businesses can port local, mobile, freephone (1800), and local‑rate (13/1300) numbers between carriers. The ACCC directs ACMA to include portability rules in the Numbering Plan, and industry codes set out the operational procedures and targets. For local numbers, the current code targets generally require telcos to complete:
Complex or multi‑number services can take longer. For 13/1300/1800, procedures are defined under the Inbound Number Portability (INP) Code.
Australian number types. SIP trunking providers can supply local geographic numbers (02, 03, 07, 08), national numbers (13/1300), and toll‑free numbers (1800); some providers also offer Australian mobile numbers. 13/1300/1800 services are inbound voice numbers. Note that 13/1300/1800 must not be used for outbound calling line identification (CLI); present a geographic or mobile CLI for outbound calls in Australia.
Cost savings. By replacing fixed‑line rentals and per‑channel ISDN fees with pay‑as‑you‑go or per‑channel SIP pricing, businesses eliminate wasted spend on unused capacity. Long‑distance and international call rates are typically far lower over SIP than legacy tariffs, with some analyses citing savings exceeding 50% on international traffic.
Scalability. Unlike ISDN, which required physical provisioning of new circuits, SIP trunking lets you add or remove channels on demand. A contact centre preparing for a seasonal spike can scale up in minutes, not weeks.
Disaster recovery and redundancy. SIP trunks can be configured with automatic failover, rerouting calls to backup locations or mobile devices if your primary site goes down. This level of resilience was difficult and expensive to achieve with traditional telephony.
HD voice quality. SIP supports high‑definition voice codecs like G.722, which deliver noticeably clearer audio than standard PSTN calls. Paired with a private or well‑managed network, this translates to a better experience for both employees and customers.
Not all SIP trunking providers are created equal, especially when serving Australian businesses that need local compliance, low latency, and reliable support. The table below summarises key evaluation criteria.
| Criteria | What to look for | Why it matters |
|---|---|---|
| Network infrastructure | Private IP backbone with regional points of presence | Reduces latency; avoids the unpredictability of the public internet |
| Australian number coverage | Local (02/03/07/08), national (13/1300), toll‑free (1800), mobile | Ensures you can provision the number types your customers expect |
| Regulatory compliance | ACMA compliance, emergency (000) support, IPND data handling | Protects your business and ensures service continuity |
| Pricing model | Pay‑as‑you‑go or per‑channel with transparent fees | Avoids overcommitting to capacity; eliminates hidden charges |
| Support | 24/7 technical support with SIP expertise | Minimises downtime, especially across Australian time zones |
Legacy telcos in Australia historically charged per‑channel fees for ISDN, often bundled into 10‑ or 30‑channel increments. This meant businesses paid for capacity they rarely used in full.
Modern SIP trunking providers offer two main pricing models. Metered (pay‑as‑you‑go) pricing charges per minute of usage, typically ranging from less than one cent to a few cents per minute depending on the destination, ideal for variable or lower volumes. Unlimited or per‑channel pricing charges a flat monthly fee per concurrent call path (often USD 15–30 per channel) and works well for consistent, high‑volume traffic. Watch for add‑ons such as number porting fees, emergency services surcharges, and setup charges. A transparent provider publishes pricing for standard configurations.
If your business is still running any legacy voice services, or if you're consolidating multiple carriers onto a single SIP platform, the migration process follows a predictable path.
Audit your current environment. Document all existing voice lines, phone numbers, PBX hardware, and how each is used. Identify any services running over legacy circuits, fax machines, alarm systems, lift phones, that may need special handling.
Choose a provider and plan your numbers. Select a SIP trunking provider that covers your Australian number requirements and submit porting requests for existing numbers. Confirm your PBX is SIP‑compatible, or plan for a gateway device if you're running older TDM equipment. Align on emergency calling configuration (000) and outbound CLI presentation.
Test before cutover. Run parallel testing with your new SIP trunks alongside existing services. Validate call quality, codec compatibility, failover behaviour, and emergency call routing before committing to a full migration.
Complete the cutover. Once testing is successful, port your numbers to the new provider and decommission legacy lines. Monitor call quality metrics closely during the first few weeks to catch any issues early.
Telnyx operates a private, multi‑cloud IP network with points of presence across the Asia‑Pacific region, including a dedicated PoP in Sydney. This keeps Australian voice traffic on a managed backbone rather than traversing the unpredictable public internet, delivering lower latency and more consistent call quality.
Telnyx provides Australian local, national, and toll‑free numbers with transparent porting and usage‑based pricing, no long‑term contracts or hidden surcharges, so businesses pay only for what they use.
For organisations using Microsoft Teams, Telnyx provides SIP trunking for Microsoft Teams through Direct Routing, enabling Teams users to make and receive PSTN calls using Telnyx as the underlying carrier. Developers building programmable voice applications can also integrate SIP trunking with the Telnyx Voice API for custom call flows, IVR systems, and real‑time voice features.
To explore Telnyx's global network coverage and Australian number availability, visit the global numbers page.
