Layla UsmanYour ISDN Lines Are Being Switched Off. Here Is What to Do About It.
If your Australian business is still running its phone system on ISDN (Integrated Services Digital Network) or PSTN (Public Switched Telephone Network) lines, there is an urgent and unavoidable reality you need to plan for: these legacy telephone services are being progressively decommissioned across Australia as the national telecommunications infrastructure transitions to IP-based technology.
The Australian Communications and Media Authority has been tracking this transition for years, and Telstra’s network modernisation programme is progressively retiring the copper and ISDN infrastructure that millions of Australian businesses have relied on. For businesses that have not yet planned their transition, the question is not whether they will need to move — it is whether they will do it proactively and on their own terms, or reactively when they have no choice.
The good news: for businesses that have already invested in a functioning on-premise PBX — whether it is a Cisco, Avaya, NEC, Panasonic, Mitel or any other platform — you do not necessarily need to replace it. You can keep your existing hardware and simply replace your ISDN lines with SIP trunks — a move that typically cuts your phone bill by 40 to 60 percent while future-proofing your communications infrastructure for the years ahead.
At BroadConnect, we have been providing SIP trunking services to Australian businesses of all sizes for over 30 years. This blog explains exactly what SIP trunking is, how it works, what it costs and whether it is the right move for your business.
| ⏰ Urgency Check: If your business relies on ISDN lines and you have not begun planning your transition to SIP or a cloud phone system, contact BroadConnect now. The timeline for ISDN availability in many Australian regions is shrinking — and a forced migration under deadline pressure is significantly more disruptive than a planned one. |
1. What Is SIP Trunking? The Plain-English Explanation
SIP trunking is one of those technology terms that sounds more complex than it actually is. Here is what it means in plain language.
The Old Way — ISDN Lines
Your office has a PBX (the box that manages your phone extensions). That PBX connects to the telephone network via physical ISDN or PSTN lines — copper cables that carry analogue or digital voice signals. You pay line rental for each of those channels, plus per-minute charges for calls. The more simultaneous calls you want to support, the more lines you rent.
The New Way — SIP Trunks
SIP (Session Initiation Protocol) is the technology that allows voice calls to be made and received over the internet, rather than over physical copper lines. A SIP trunk is essentially a virtual telephone line — a connection between your existing PBX and the public telephone network, delivered over your internet connection.
Your PBX stays exactly where it is. Your phone numbers stay the same. Your extensions, your IVR menus, your hold music — all unchanged. The only thing that changes is how your PBX connects to the outside world: copper lines replaced by a high-quality internet-based connection that is dramatically cheaper, more flexible and more capable.
| 🔧 Technical Analogy: Think of your PBX as a factory, and your phone lines as the roads connecting it to customers. ISDN lines are like renting a fixed number of lanes on a toll road — you pay for each lane whether traffic is running or not. SIP trunks are like switching to a motorway where you only pay for the lanes you use, can add more instantly, and the road never wears out. |
| Feature | ISDN / PSTN Lines | BroadConnect SIP Trunking |
|---|---|---|
| Infrastructure | Physical copper cables — limited by physical capacity | Virtual — delivered over your business internet connection |
| Line rental cost | $30–$80 per channel per month | Significantly lower — concurrent call pricing |
| Call charges | Per-minute STD and mobile charges | Competitive flat rates or unlimited options |
| Scalability | Add a line = technician visit + new hardware | Add a concurrent channel in minutes — via portal |
| Geographic number flexibility | Tied to physical location of copper | Numbers ported — keep existing numbers regardless of location |
| Redundancy | Physical line failure = outage | Automatic failover to mobile or secondary internet |
| Existing PBX | Required — ISDN connects to your PBX | Kept — SIP trunk connects to your existing PBX |
| Future availability | Being decommissioned across Australia | Future-proof IP technology — not facing retirement |
| Monthly total (typical 10-channel office) | $600–$1,200/month | $200–$450/month |
2. How SIP Trunking Works With Your Existing Phone System
One of the most common misconceptions about SIP trunking is that it requires replacing your existing phone system. For the vast majority of modern business PBX platforms, this is simply not true. Here is how the connection works:
- Your PBX receives a SIP trunk connection: BroadConnect provisions a SIP trunk — a virtual connection — configured to work with your specific PBX make and model
- Your existing numbers are ported: All your current business phone numbers are transferred to BroadConnect’s SIP platform — callers continue dialling the same numbers
- Calls route via your internet connection: Inbound and outbound calls travel over your business internet rather than copper lines — same call quality, lower cost
- Your PBX manages extensions as normal: Every existing extension, hunt group, IVR menu and feature of your PBX continues to work exactly as before
- Concurrent channels scale on demand: Need to handle 15 simultaneous calls instead of 10? Add concurrent channels via the BroadConnect portal in minutes — no technician needed
Compatible PBX Platforms
BroadConnect SIP trunks are compatible with all major business PBX platforms used in Australia:
| PBX Brand | Compatibility | Notes |
|---|---|---|
| Cisco (CUCM, Business Edition, CME) | ✅ Full compatibility | SIP configuration supported across all Cisco PBX platforms |
| Avaya (IP Office, Communication Manager) | ✅ Full compatibility | BroadConnect has extensive Avaya SIP trunk experience |
| NEC (SV9100, SV8100, SV8300) | ✅ Full compatibility | Popular in Australian healthcare and education — fully supported |
| Panasonic (NS700, NS1000) | ✅ Full compatibility | Common in Australian SMB environments — SIP trunk ready |
| Mitel (MiVoice) | ✅ Full compatibility | BroadConnect-certified Mitel SIP trunk configuration |
| 3CX | ✅ Full compatibility | BroadConnect is a 3CX-compatible SIP trunking provider |
| Asterisk / FreePBX | ✅ Full compatibility | Open-source PBX platforms fully supported |
| Other SIP-compatible PBX | ✅ Generally compatible | Any PBX with a SIP trunk interface — BroadConnect will test compatibility before deployment |
Not sure if your PBX is compatible? Contact BroadConnect for a free compatibility assessment — our technical team will confirm compatibility and provide a full cost comparison before you commit to anything.
3. The Real Numbers: What SIP Trunking Saves Australian Businesses
The financial case for SIP trunking is one of the clearest in all of business technology. Here are the three areas where savings materialise — and what they typically look like for Australian businesses.
Area 1: Line Rental Savings
ISDN BRI and PRI lines carry significant monthly line rental charges per channel — regardless of whether you are using them. SIP trunking charges for concurrent call capacity, typically at a much lower per-channel rate, with the ability to burst above your contracted capacity for short periods rather than paying for permanent channels that sit idle.
| Office Size | Typical ISDN Cost | BroadConnect SIP Cost | Monthly Saving | Annual Saving |
|---|---|---|---|---|
| Small (5 concurrent channels) | $250–$450/month | $80–$150/month | $150–$300/month | $1,800–$3,600 |
| Medium (10 concurrent channels) | $500–$900/month | $160–$280/month | $300–$650/month | $3,600–$7,800 |
| Large (20 concurrent channels) | $1,000–$1,800/month | $300–$500/month | $600–$1,300/month | $7,200–$15,600 |
| Multi-site (3 offices, 30 ch.) | $1,800–$3,200/month | $450–$750/month | $1,200–$2,500/month | $14,400–$30,000 |
Area 2: Call Rate Savings
ISDN call charges — particularly for mobile calls and STD calls — are often significantly higher than VoIP call rates. BroadConnect’s SIP trunking includes highly competitive call rates that typically save 30–50% on call charges compared to ISDN tariffs. For businesses with high outbound call volumes — call centres, sales teams, healthcare practices — this alone can justify the transition.
Area 3: Scalability Savings
With ISDN, adding a new concurrent call channel requires a physical line order, a technician visit and lead time of days or weeks. With SIP trunking, concurrent channels can be added in minutes via the BroadConnect portal — at a lower per-channel cost. For growing businesses, this eliminates the perpetual cycle of capacity planning, over-provisioning and lead-time delays.
| 💰 Real Client Example: A 12-line medical centre in suburban Sydney was paying $1,100/month for ISDN lines and call charges. After migrating to BroadConnect SIP trunking — keeping their existing NEC PBX — their monthly communications cost dropped to $380/month. Annual saving: $8,640. Implementation time: 5 business days. |
4. SIP Trunking vs. a Hosted Cloud Phone System: How to Choose
Both SIP trunking and a hosted cloud phone system achieve the same core goal: moving your business from ISDN to IP-based calling. But they take different approaches, and the right choice depends on your specific situation.
| Factor | SIP Trunking | Hosted Cloud Phone System |
|---|---|---|
| Your existing PBX | Keep it — SIP connects to your existing PBX | Replace it — cloud PBX is hosted and managed by BroadConnect |
| Upfront cost | Low — minimal configuration cost | Low — no hardware, monthly subscription from $35/user |
| Monthly cost | Lower — you own the PBX hardware | Slightly higher — but all maintenance and upgrades included |
| PBX maintenance | Your responsibility — you own the hardware | BroadConnect’s responsibility — fully managed |
| Remote work capability | Limited — depends on your PBX model | Full — softphone app works from any device anywhere |
| Microsoft Teams integration | Complex — requires additional SBC hardware | Native — built-in Teams Direct Routing available |
| Scalability | Limited by PBX capacity — hardware upgrade needed beyond capacity | Instant — add users in minutes via portal |
| Features | Whatever your PBX supports | Full modern feature set — call recording, analytics, IVR, etc. |
| Best for | Businesses with recent PBX investment wanting to reduce line costs and extend PBX life | Businesses ready for full modernisation or with ageing/end-of-life PBX hardware |
| Migration effort | Low — keep PBX, just replace lines | Medium — full migration but BroadConnect manages end-to-end |
The practical rule: if your PBX is less than 5 years old and still functioning well, SIP trunking is likely the right first step — extend its life while dramatically reducing your line costs. If your PBX is more than 7–8 years old, approaching end-of-support or lacking modern features like softphones and remote work capability, a full migration to a hosted cloud phone system is worth considering. BroadConnect will help you make the right call — free assessment.
5. Will SIP Trunking Be as Reliable as Our Current ISDN Lines?
This is the most common concern Australian businesses raise when considering SIP trunking — and it is a fair question. ISDN has been reliable for decades. The copper line either works or it does not, and when it works, call quality is consistent.
The honest answer to whether SIP trunking matches ISDN reliability is: with the right setup, yes — and in several important ways, it actually exceeds it.
| Reliability Factor | ISDN Lines | BroadConnect SIP Trunking (Properly Configured) |
|---|---|---|
| Call quality | Consistent but limited to ISDN codec quality | Equal or superior — HD voice codecs available (G.722) |
| Single point of failure | Physical cable fault = complete outage | Automatic failover to mobile or secondary internet — business continues |
| Internet dependency | Independent — works without internet | Requires reliable business internet — BroadConnect provides this too |
| Jitter / packet loss | N/A — circuit-switched | Managed via QoS configuration — voice traffic prioritised on your network |
| Network monitoring | Telstra monitors the line | BroadConnect monitors SIP trunk health 24/7 — proactive alerts |
| Fault response | Physical line fault can take 24–72 hours to repair | Configuration issues resolved remotely — typically within hours |
| Disaster recovery | No built-in failover — physical damage = outage | Calls reroute to mobiles instantly if primary internet fails |
The key to SIP trunking reliability is the quality of the underlying internet connection and its configuration. BroadConnect strongly recommends — and can provide — a Business NBN or fibre connection with QoS (Quality of Service) configured to prioritise voice traffic, alongside a 4G/5G failover solution as an automatic backup. Together, this creates a SIP trunking environment that is more resilient than ISDN — not less.
6. The ISDN Switch-Off: Why the Clock Is Already Ticking
Australia’s legacy PSTN and ISDN network infrastructure is being progressively retired as the country’s telecommunications moves entirely to IP-based delivery. This transition has been underway for years, and Telstra’s published network modernisation roadmap confirms that legacy circuit-switched services are being systematically withdrawn.
What this means practically for your business:
- Your ISDN service has an end date. Whether that date is 12 months or 3 years away depends on your specific location and exchange. In many Australian regions, the window is shorter than businesses realise.
- Forced migrations are more disruptive than planned ones. Businesses that wait until they receive a ‘service end’ notice from Telstra face compressed timelines, higher demand for migration support and the risk of disruption during the cutover window.
- Equipment supply is shrinking. ISDN hardware is becoming harder and more expensive to source for maintenance. Systems that fail during the transition window may not be easily repaired.
- SIP trunking lead time is short. BroadConnect can typically have a SIP trunk active and your numbers ported within 5–10 business days — but planning and assessment should begin well in advance.
| 🚨 Action Required: If your business is on ISDN and you have not yet begun your migration planning, contact BroadConnect today for a free ISDN transition assessment. We will confirm your timeline exposure, assess your PBX compatibility and provide a migration plan and cost comparison — at no cost and with no obligation. |
7. Multi-Site Businesses: How SIP Trunking Unifies Your Communications
For businesses with multiple offices across Australia, SIP trunking with BroadConnect’s SD-WAN creates a powerful unified communications environment — one where all sites share the same SIP trunk capacity, the same number ranges and the same management infrastructure.
Here is how multi-site SIP trunking works:
| Multi-Site Capability | With ISDN (Current) | With BroadConnect SIP Trunking |
|---|---|---|
| Inter-site calls | External call between sites — charges apply | Free internal calls between all sites — no PSTN charges |
| Shared call capacity | Each site has fixed ISDN channels — no sharing | Centralised SIP trunk pool — capacity shared across all sites |
| Number portability | Geographic numbers tied to physical locations | All numbers portable — Brisbane office can use a Sydney 02 number |
| Central management | Each site managed separately — no unified view | One BroadConnect portal — all sites, all numbers, all usage |
| Overflow between sites | Not possible — each site has independent lines | Calls can overflow from a busy site to available agents at another site |
| Disaster recovery | Site outage = that site’s phones are down | Site outage — calls reroute to another site or mobiles automatically |
| Centralised billing | Separate ISDN invoices per site — complex to reconcile | One BroadConnect invoice for all sites — simplified billing |
For a business with three or more Australian offices, the savings from eliminating inter-site call charges alone — calls that currently traverse the PSTN and incur STD charges — often exceed the total cost of the SIP trunking service. The additional benefit of shared capacity and centralised management compounds the value further.
8. The BroadConnect SIP Trunking Migration — What to Expect
Migrating from ISDN to SIP trunking with BroadConnect is a straightforward process that BroadConnect manages end-to-end. Here is exactly what happens:
| Stage | Timeframe | What BroadConnect Does | What You Need to Provide |
|---|---|---|---|
| 1. Technical Assessment | Day 1–2 | Confirm PBX make/model/version; test SIP compatibility; assess internet connection quality; identify number porting requirements | PBX model and firmware version; current phone number list; internet connection details |
| 2. Proposal | Day 2–3 | Provide detailed cost comparison (ISDN vs. SIP); recommend concurrent channel count; identify any PBX configuration changes needed | Review and approve the proposal |
| 3. Number Porting Order | Day 3–8 | Lodge all phone number porting requests with relevant carriers; manage the porting process from end to end | Sign porting authority documents — BroadConnect handles the rest |
| 4. SIP Trunk Provisioning | Day 3–7 | Provision BroadConnect SIP trunk; configure Session Border Controller; prepare SIP credentials for your PBX | Minimal — BroadConnect does the technical work |
| 5. PBX Configuration | Day 7–12 | Connect the SIP trunk to your PBX; configure dial plans, call routing and failover rules; test all inbound and outbound call scenarios | Brief access to PBX for configuration — usually IT admin access |
| 6. Testing | Day 12–13 | Full end-to-end testing — all numbers, all call types, all routing scenarios; quality testing with HD codec where available | Participate in brief test call verification |
| 7. Cutover | Day 14 | Numbers ported and live on SIP trunk; ISDN lines decommissioned; monitoring active on new SIP infrastructure | Communicate internally that changeover is occurring |
| 8. Ongoing | Always | 24/7 SIP trunk monitoring; proactive alerts on quality issues; rapid response to faults; account management for changes | Call BroadConnect if anything changes — 1300 880 330 |
Most BroadConnect SIP trunking migrations are completed within 10 to 14 business days. Your phone numbers remain the same. Your PBX features remain unchanged. Your ISDN costs disappear. And from day one, you are future-proofed against the ISDN switch-off.
9. Why BroadConnect for SIP Trunking — Not a Generic VoIP Provider
The SIP trunking market is crowded with providers — from global wholesale carriers to small local resellers. Here is why BroadConnect is the right choice for Australian businesses:
| Generic VoIP / SIP Providers | BroadConnect SIP Trunking |
|---|---|
| Sell SIP trunks only — no holistic view of your communications | Full-service provider — SIP trunk + internet + phone system + mobile, all from one Australian team |
| Limited PBX expertise — configuration left to your IT team | 30+ years of PBX and telephony experience — BroadConnect configures the SIP integration for you |
| No account manager — support via ticketing system | Dedicated Australian account manager — one person who knows your setup |
| Offshore technical support — unfamiliar with Australian telephony environment | Australian technical team — understands local carriers, number formats and regulatory requirements |
| SIP trunking only — can’t help with internet quality or failover | End-to-end solution — SIP + Business NBN + 4G/5G failover as an integrated package |
| Pricing in USD or unclear AUD equivalents | Transparent AUD pricing — no exchange rate exposure, no hidden fees |
| Generic contracts with unclear termination terms | Clear, month-to-month terms with straightforward migration support if you ever need to change |
| No pathway to cloud phone system if you later want to upgrade | Seamless upgrade path to BroadConnect hosted cloud phone system — same provider, same account manager |
BroadConnect is not simply a SIP trunk reseller. We are a full-service Australian communications provider that happens to offer SIP trunking as one of more than ten services — all designed to work together and all supported by the same Australian team that has been in this industry since 1990. Contact BroadConnect for a free SIP trunking assessment.
10. Frequently Asked Questions
Q: Our PBX is quite old. Will SIP trunking still work?
It depends on the specific PBX. Most business PBX platforms manufactured in the last 10–12 years have SIP trunk capability — either natively or via a software upgrade. BroadConnect’s technical team will confirm compatibility before any work begins, at no cost. If your PBX is genuinely too old to support SIP trunking, we will tell you honestly — and present the hosted cloud phone system as the better path forward, along with a full cost comparison.
Q: What internet connection do we need for SIP trunking?
SIP trunking requires a stable, business-grade internet connection with sufficient bandwidth and low latency. A single HD voice call uses approximately 100 Kbps. A 10-channel SIP trunk (10 simultaneous calls) needs around 1 Mbps dedicated to voice. BroadConnect strongly recommends a Business NBN plan with QoS configuration for voice traffic, and a 4G/5G failover backup. If needed, we can upgrade your internet connection and implement SIP trunking simultaneously.
Q: Can we keep our existing phone numbers?
Yes — number porting is a standard part of every BroadConnect SIP trunking migration. All Australian geographic numbers (02, 03, 07, 08), 1300/1800 numbers and DDI ranges can be ported to BroadConnect’s SIP platform. Callers continue dialling the same numbers with no interruption. The porting process typically takes 5–10 business days and is managed entirely by BroadConnect.
Q: What happens if our internet connection goes down?
BroadConnect configures automatic failover as part of every SIP trunking deployment where the customer also has a 4G/5G backup connection. If the primary internet fails, inbound calls are automatically rerouted to nominated mobile numbers or a secondary internet connection — within seconds. This actually makes a SIP-based setup more resilient than a standard ISDN arrangement, which has no built-in failover whatsoever.
Q: We are a business with offices in multiple states. Can BroadConnect manage SIP trunking across all our sites?
Yes — multi-site SIP trunking is one of BroadConnect’s strongest capabilities. All sites are managed under a single account with a single account manager, consolidated billing and unified monitoring. Inter-site calls are free. Capacity can be shared across sites. And the entire multi-site environment is visible from a single BroadConnect management portal. Contact BroadConnect to discuss your multi-site requirements.
Conclusion: SIP Trunking Is the Smartest Move Most Australian Businesses Haven’t Made Yet
The combination of the ISDN switch-off deadline, significant cost savings and the ability to keep your existing PBX makes SIP trunking one of the most financially compelling technology decisions available to Australian businesses right now. You do not need to replace your phone system. You do not need to disrupt your operations. You just need to replace your ISDN lines with a better, cheaper, more reliable alternative — before the switch-off forces your hand.
BroadConnect has been making this transition seamless for Australian businesses for over 30 years. Our technical expertise, our Australian support team and our full-service approach — combining SIP trunking, business internet and failover into a single managed solution — means the transition is handled end-to-end, with minimal disruption and maximum savings from day one.
The free ISDN transition and SIP trunking assessment takes 30 minutes. The savings last for years. Book yours at broadconnect.com.au/contact-us or call 1300 880 330 today.
References & Further Reading
- BroadConnect SIP Trunking — Australian Business
- BroadConnect Hosted Cloud Phone System
- BroadConnect Business NBN Plans
- BroadConnect 4G/5G Internet & Failover
- BroadConnect Managed Network & SD-WAN
- Australian Communications and Media Authority — Network Transition
- Telstra — Network Modernisation Programme
- Australian Bureau of Statistics — Business Technology
- BroadConnect — Free SIP Trunking Assessment
- BroadConnect — Full Services Overview
| Replace ISDN. Keep Your PBX. Cut Your Bill by Up to 60%.BroadConnect SIP Trunking — compatible with all major PBX brands. Live in 14 days.Free ISDN transition assessment — no obligation, real savings from day one.Call 1300 880 330 | Mon–Fri 8am–5pm | hello@broadconnect.com.au>>> Book Your Free SIP Assessment — broadconnect.com.au <<< |