How to Cut Your Business Phone Bill by 40% with SIP Trunking

If your Melbourne business is still running on traditional phone lines, there’s a good chance you’re paying more than you need to. A lot more.

SIP trunking for Melbourne businesses has become one of the most practical ways to slash telecommunications costs, often by 40% or more, without ripping out your existing phone system. The technology works by replacing your old physical lines with internet-based voice connections, and the savings are real.

In this guide, you’ll learn exactly what SIP trunking is, how much Melbourne businesses typically save, whether your current setup is compatible, what your network needs to handle it, and how to make the switch step by step. Everything you need to make a confident decision in 2025.

What Is SIP Trunking?

SIP stands for Session Initiation Protocol. It’s the technology that manages how voice calls are set up, maintained, and ended over the internet. A SIP trunk is essentially a virtual phone line, an internet-based connection that replaces the old copper-wire PSTN lines most Australian businesses have relied on for decades.

Instead of physical lines running into your building, your phone system connects to a VoIP provider over your broadband or fibre connection. Calls travel as data packets, the same way your emails and video calls do.

Here’s why this matters for Australian businesses: Telstra has already shut down its ISDN network. ISDN services across Australia were exited by mid-2022, with Telstra’s underlying platforms ceasing to be supported by vendors. That means if you’re still on legacy PSTN or ISDN lines, your options are narrowing fast. 

SIP trunking is the modern replacement. It works with your existing PBX phone system (including popular systems like 3CX, Cisco, Avaya, and Mitel), which means you may not need to replace a single desk phone.

Key terms to know:

Term	What it means
SIP trunk	A virtual phone line delivered over the internet
Channel / concurrent call	One active call at a time per channel
PBX	Your internal phone switching system
PSTN	The old public switched telephone network
Number porting	Moving your existing phone numbers to a new provider

How Much Can Melbourne Businesses Save with SIP Trunking?

This is the question most Melbourne business owners want answered first, and the numbers are genuinely compelling.

Industry analysis consistently shows that businesses migrating from PRI or ISDN to SIP trunking reduce monthly voice costs by 30 to 60%. Some businesses report even higher savings depending on their call volume and existing tariff structure. 

The savings come from a few different places:

• Line rental charges disappear. Traditional PSTN and ISDN services carry fixed line rental fees regardless of how much you use them. SIP trunks are typically priced per channel, so you only pay for what you actually need.
• Call rates drop significantly. Long-distance and international calls that once carried premium rates are dramatically cheaper when routed over the internet.
• You consolidate your invoice. Instead of multiple line items from different carriers, SIP trunking often brings everything into a single, predictable monthly bill.
• Line rental charges are eliminated. With no physical copper to maintain, those recurring line rental costs simply go away.

Where the savings come from:

Cost category	Traditional PSTN	SIP Trunking
Line rental	Per line, recurring	Eliminated
Local calls	Fixed tariff	Reduced or included
Long-distance calls	Premium rate	Significantly lower
International calls	High per-minute rates	Substantially cheaper
Scaling costs	New physical line required	Add a channel instantly

Real savings add up quickly for businesses with moderate to high call volumes. A Melbourne business running, say, 10 to 20 concurrent channels will see the difference on their very first invoice.

For businesses of all sizes, the shift to SIP delivers significant cost savings on both the line rental and call rates side of the ledger. The total cost of telephony goes down, and it usually stays down.

Does Your Current Phone System Support SIP Trunking?

Good news: most modern PBX systems already support SIP trunking, or can be upgraded to do so without major cost.

Compatible systems include:

• 3CX (fully SIP-native, widely used across Melbourne)
• Cisco Unified Communications Manager
• Avaya IP Office
• Mitel MiVoice
• Most IP-enabled on-premise PBX systems from the last decade

How to check if your existing phone system qualifies:

1. Check whether your PBX has a SIP trunk configuration option (most do)
2. Ask your current telephony provider whether your system supports SIP lines
3. If you’re on a legacy analogue or digital system, a SIP gateway device can bridge the gap, meaning you can keep your existing phones and handsets

If you’re on a hosted business VoIP platform or a cloud PBX, you may already be using SIP trunking without knowing it.

What about older systems?

Businesses still running older ISDN lines or legacy copper-based setups will need to transition to SIP, but this doesn’t have to mean replacing everything. A SIP gateway lets you connect your current desk phones to a modern SIP provider, preserving your investment while cutting costs.

The migration process is more straightforward for businesses already on an IP-enabled PBX. For everyone else, Telco ICT can assess your current setup and recommend the most cost-effective path forward.

Network Requirements for SIP Trunking

SIP trunking runs over your internet connection, so the quality of your calls depends on the quality of your network. The good news is that most Melbourne businesses on the NBN or a dedicated fibre connection already have more than enough bandwidth.

Bandwidth requirements:

Each concurrent call uses roughly 80 to 100 Kbps of bandwidth (depending on the codec). Here’s a quick reference:

Concurrent channels	Minimum bandwidth needed
5	0.5 Mbps
10	1 Mbps
20	2 Mbps
50	5 Mbps

Most business NBN plans run at speeds well above this. However, bandwidth is only part of the equation.

What actually affects call quality:

• Latency: Delays in data transmission cause noticeable lag in conversation. Aim for under 150ms round-trip.
• Jitter: Inconsistent packet delivery creates choppy audio. Jitter should be below 30ms.
• Packet loss: Even 1 to 2% packet loss can noticeably degrade call quality.

Network setup recommendations:

• Use a router with Quality of Service (QoS) settings to prioritise voice traffic over general internet use
• Consider a dedicated VLAN for voice routing if your business runs heavy data workloads
• For critical telephony environments, a dedicated internet circuit for voice is worth the investment
• Configure failover using 4G/5G backup so calls continue even if your fixed broadband drops

Connectivity checklist before switching:

• Test your current upload and download speeds
• Check jitter and latency with a VoIP readiness test
• Confirm your router supports QoS
• Discuss failover options with your provider

Step-by-Step: How to Switch to SIP Trunking

The transition to SIP is a straightforward process for most Melbourne businesses, particularly those already on an IP-capable phone system. Here’s how it typically works.

Step 1: Audit your current phone bill

Pull out your last two or three months of invoices. Look at:

• How many PSTN lines or ISDN connections are you paying for
• Your concurrent calls peak usage (how many calls happen at the same time)
• Your outbound call volumes, especially long-distance and international calls
• Any line items you’re paying for but not using

This gives you the baseline to measure your real savings.

Step 2: Assess your phone system compatibility

Work out whether your current PBX supports SIP trunking natively or needs a gateway. Check your system’s documentation or ask your ICT provider. Most systems from the last ten years do support it, including softphones and desktop clients.

Step 3: Choose the right number of channels

The size of your business and typical call volumes will determine how many SIP lines you need. A general rule: count the maximum number of simultaneous calls your business makes during peak hours, then add a small buffer. This is what you mean by per-channel pricing: you only pay for the capacity you actually use.

Step 4: Plan your number porting

Number porting lets you keep your existing phone numbers when you switch providers. This is a critical step that needs to be planned carefully to avoid any gap in service. Your new SIP provider manages the port request with your current carrier. The process typically takes a few days to a couple of weeks, depending on your current provider.

Step 5: Configure your network

Before going live, work with your provider to configure QoS on your router, set up failover, and test call quality end-to-end. This is also the time to set up call analytics, call recording if required, and routing rules.

Step 6: Test, then go live

Run both systems in parallel briefly if possible, particularly for inbound calls. Test with real voice calls on different devices, including any softphones. Once you’re satisfied, cut over completely and cancel your legacy lines.

Step 7: Review your first invoice

Compare your first SIP trunking bill against your old PSTN spend. For most Melbourne businesses, the difference is immediately visible.

Ready to Find Out What Your Business Could Save?

If you’re still paying for legacy PSTN lines, there’s a real case for reviewing your spend now. The SIP trunking market in Australia has matured significantly, SIP providers are competitive, and Melbourne businesses are already putting those savings to work elsewhere in their operations.

Telco ICT Group offers a free phone bill audit and savings estimate. We’ll look at your current invoice, assess your existing phone system, and give you a clear picture of what switching to SIP trunking could save you.

Call 1300 414 214 or visit us to get started.

Frequently Asked Questions

Will I keep my existing phone numbers when switching to SIP trunking?
Yes. Number porting lets you transfer your current business numbers across to your new SIP trunk. Telco ICT handles the entire porting process to make sure there’s no gap in service.

What happens to my calls if the internet goes down?
With failover configured via 4G/5G, calls automatically re-route through the mobile network if your fixed connection drops. Telco ICT includes a failover setup in all SIP trunk installations.

Is SIP trunking secure?
Yes, when properly configured. SIP calls should be encrypted using TLS/SRTP protocols. Telco ICT configures all SIP trunks with appropriate encryption and fraud prevention settings from day one.

How many SIP channels does my business need?
A good starting point: count the maximum number of simultaneous calls your business handles during peak times. Add a small buffer for growth. Concurrent channels are priced individually, so you’re not paying for capacity you don’t use.

Is SIP trunking suitable for small businesses?
Absolutely. Business VoIP via SIP trunking is one of the most cost-effective options for small and mid-size businesses. You only pay for what you use, and it scales easily as your business needs grow. The SIP trunking market now serves businesses of all sizes across Australia, from sole traders to enterprises.