SIP vs VoIP Explained: What Australian Businesses Actually Need to Know (2026)

You will encounter both "VoIP" and "SIP" when researching business phone systems. They are related but different things, and understanding the relationship stops you making common mistakes like buying a "VoIP phone" that turns out to need specific configuration to work with your provider, or choosing a "SIP trunk" without understanding it does not include a phone system.

The short version: VoIP (Voice over Internet Protocol) is the broad category of technology that transmits voice over IP networks, which may include the public internet or private and managed networks. SIP (Session Initiation Protocol) is an open signalling standard used to establish and manage VoIP calls and other multimedia sessions. All SIP calls are VoIP calls, but not all VoIP calls use SIP.

What VoIP Means

VoIP stands for Voice over Internet Protocol. It is the general term for transmitting voice using Internet Protocol over an IP network, which may be private, managed, or connected through the public internet. When your NBN modem has a green phone port that your old handset plugs into, the calls going over that port are VoIP. When a staff member uses a softphone on their laptop to call a client, that is VoIP. When a call centre uses an IP phone system, that is VoIP.

VoIP is a broad technology category, not a specific product. It describes the approach (calls over IP networks) rather than the specific method used. Under the VoIP umbrella, there are several different protocols and approaches: SIP is one, H.323 is another (older, used in video conferencing systems), Microsoft Teams uses its own proprietary signalling layer, and Zoom Phone uses its own protocol as well. When a provider says their product is "VoIP," they are telling you what category it is in, not what specific technology it uses.

If you're evaluating phone systems and a provider mentions 'SIP trunks', 'SIP phones', or 'hosted SIP', they are describing the technology your calls will run on. SIP is used by modern business phone systems, while some platforms use other signalling internally or expose SIP only through supported interfaces and gateways. Understanding the term helps you ask the right questions and avoid buying hardware that locks you to one provider.

You do not need to understand SIP in depth to use a cloud phone system. The practical difference is this: If your provider supports your exact SIP phone model and permits the required provisioning method, you may be able to reuse the phone; confirm model, firmware, certificate, and provisioning requirements first. If a provider gives you a proprietary phone that only works with their system, you lose the ability to change providers without replacing your hardware. Knowing the difference saves you from this common lock-in.

What SIP Means

SIP stands for Session Initiation Protocol. It is a signalling standard used to establish, manage, and terminate calls and other multimedia sessions. SIP handles the signalling part of a call: ringing, answering, putting on hold, transferring, and hanging up. Once the call is connected, the actual audio typically travels over a separate protocol called RTP (Real-time Transport Protocol).

SIP is an open standard, which means any provider or hardware vendor can implement it. A SIP-compatible phone from Yealink will work with a SIP trunk from Telnyx, connected to a 3CX PBX or a FreePBX system, because all three are implementing the same SIP standard. This interoperability is one of the main practical advantages of the SIP ecosystem over proprietary systems.

When a business buys a "SIP phone" or a "SIP desk phone," they are buying a phone that implements SIP and may register with a compatible PBX or hosted PBX service when the exact model, firmware, security, authentication, and provisioning requirements are supported. When a provider sells a "SIP trunk," they are selling a carrier service that uses SIP to connect your PBX to the public phone network.

The Relationship Between SIP and VoIP

The relationship between SIP and VoIP is the same as between TCP and internet communication: TCP is one specific protocol used to send data over the internet, and the internet includes other protocols as well. SIP is a signalling protocol that can be used in VoIP and other multimedia sessions; VoIP also uses media and transport protocols and can use signalling other than SIP.

In practice for Australian businesses, this means:

• When a provider says their phone or service is "VoIP," ask whether it is specifically SIP-based. SIP is used in Australian business VoIP, but platform interoperability varies: services such as Microsoft Teams, Zoom Phone, and RingCentral support SIP devices or trunks only through their documented compatibility and provisioning paths.
• A SIP phone may work with an Australian hosted PBX when the provider supports its exact model, firmware, security requirements, and provisioning method; a SIP trunk normally connects to a PBX rather than directly to an ordinary desk phone. A Microsoft Teams-certified phone may only work with Teams.
• A "SIP trunk" from an Australian carrier connects to a SIP-based PBX. It will not work directly with a Microsoft Teams Phone Calling Plan setup without a Session Border Controller in between.

When the SIP vs VoIP Distinction Matters in Practice

When buying hardware

If you are buying IP desk phones, confirm whether they are standard SIP phones or proprietary phones locked to a specific platform. A Yealink T46U or Grandstream GRP2614 is a standard SIP phone, but compatibility and support depend on the provider, exact firmware, certificates, and provisioning requirements. A Microsoft Teams-certified phone is designed specifically for the Teams ecosystem and requires a Microsoft Teams Phone licence to function as a business phone.

Standard SIP phones can offer configuration and provider flexibility, but portability still depends on the exact model, firmware, certificates, provisioning, and receiving provider's support policy. If you switch phone system providers, your SIP phones come with you. Proprietary phones may not. For a comparison of SIP desk phones suitable for Australian businesses, see our best SIP desk phone guide.

When choosing a provider

Australian hosted PBX services may use SIP, but compatibility with standard SIP phones and external trunks depends on each provider's supported-device, carrier, security, and provisioning policies. A few platforms use proprietary signalling (Microsoft Teams, Zoom Phone, some Cisco and Avaya enterprise systems). The practical difference:

• SIP-based platforms: more hardware flexibility, more carrier choice, more configuration control.
• Proprietary platforms: typically more polished consumer experience (especially Teams and Zoom), better integration with that vendor's ecosystem, but less flexibility in hardware and carrier choice.

For most Australian SMBs, a SIP-based hosted PBX (Maxotel, 8x8, RingCentral AU) with standard SIP phones is the right choice. Teams Phone makes sense if your business is already deeply invested in Microsoft 365 and has specific Teams integration requirements.

When configuring a phone system

SIP-phone setup varies by provider and may use manual server credentials, assisted or zero-touch provisioning, certificates, or an enrollment and account-pairing process. These go into the phone's configuration interface. When the phone registers successfully with these credentials, it is connected to the SIP system and can make and receive calls.

When configuring a SIP trunk on a self-hosted PBX (3CX, FreePBX), you enter the SIP trunk provider's credentials into the PBX. The PBX connects to the SIP trunk using the provider's required method, which may be registration/account-based or IP-based, and then routes calls to and from the public phone network.

When configuring Microsoft Teams Phone with Direct Routing, the process is different: a certified Session Border Controller (SBC) connects the carrier or SIP trunk to Microsoft Teams Phone's Direct Routing interface, which uses SIP over TLS for signalling and SRTP/SRTCP for media. This is more complex and is one reason many businesses choose a SIP-native hosted PBX over Teams Direct Routing unless they have a specific reason to stay in the Teams ecosystem.

When the Distinction Does Not Matter

If you are using a bundled hosted PBX service (one provider for phones, system, and calling), the SIP vs VoIP distinction is mostly invisible to you. The provider handles the SIP configuration internally. You log in to a web portal, configure your extensions, and your phones work. Whether the underlying protocol is SIP, H.323, or something proprietary is irrelevant to your daily operation.

The distinction becomes relevant again when you need to troubleshoot an interoperability issue (your phones do not register, audio drops on transfer), when you are selecting hardware that needs to be compatible with a specific system, or when you are evaluating whether a carrier or phone can be moved between providers.

Common Terminology Clarified

The Australian Business Context

In Australia, the shift from copper PSTN to NBN-based telephony has made VoIP (and specifically SIP-based VoIP) the default for business phone systems. Where legacy fixed-line services are being disconnected, migration to an NBN-based phone service is not automatic; the customer must arrange a replacement service with a phone or internet provider, and some areas and services are excluded from copper disconnection.

The green phone port on most Australian NBN modems is an ATA (Analogue Telephone Adapter) that converts analogue signals from a traditional handset into VoIP calls, using your ISP's configuration. This is VoIP, but it is not SIP in the sense that you control. The provider commonly manages the voice provisioning, while customer access, routing features, extension support, and integration options vary by provider and service. It is a residential-grade VoIP service dressed up as a landline.

A business that needs multiple lines, auto-attendant, ring groups, or call recording should choose a business phone service that explicitly provides those features, such as a hosted PBX, a self-hosted PBX with a SIP trunk, or another supported cloud phone platform. For a full explanation of what the green phone port does and why it limits business users, see our what is VoIP guide for Australian businesses.

Standard SIP phones may work with multiple Australian providers, but not necessarily out of the box; confirm the exact model, firmware, certificate, security, and provisioning requirements before purchase or migration. The interoperability of the SIP standard means you have more flexibility to mix and match hardware and providers than you would in a proprietary ecosystem.

What Most Businesses Get Wrong

Buying a phone system and then discovering the phones they already own are not compatible. A business that migrates to Microsoft Teams Phone and then discovers their existing Yealink SIP phones cannot be used (Teams supports Teams-certified devices and listed compatible SIP devices through Microsoft's SIP Gateway cloud service) has bought an expensive incompatibility. Check hardware compatibility before choosing a platform.

Using "VoIP" and "SIP trunk" interchangeably when shopping around. When asking a provider for a quote, being specific about what you need saves time. If you need a SIP trunk to connect an existing self-hosted PBX, say that. If you need a complete hosted phone system with calling included, say that. The two have completely different pricing models and the provider cannot give you a useful quote without knowing which you are after.

Assuming all VoIP phones work with all systems. Standard SIP phones are broadly compatible, but some phone models have quirks with specific PBX platforms. Before buying phones in bulk for a new phone system deployment, test one handset with your intended platform first. Check whether your intended hosted PBX provider publishes a supported or recommended phone-model list, and obtain written compatibility confirmation if it does not.

Your Next Steps

For a business evaluating VoIP/SIP options:

1. Decide whether you want a bundled hosted PBX (all-in-one, no SIP configuration) or a separate SIP trunk plus PBX (more flexibility, more configuration).
2. If buying phones, confirm they are standard SIP phones (not proprietary hardware locked to a specific platform) unless you are specifically building a Microsoft Teams or Zoom Phone environment.
3. When getting quotes, ask providers explicitly: is this a hosted PBX service, a SIP trunk, or both? Clarify what is and is not included.
4. If you are on the NBN green phone port and want a proper business phone system, that means moving to a hosted PBX service or a SIP trunk plus PBX. The green phone port is a starting point, not a business phone solution.

Once you know whether you need SIP trunking or a hosted VoIP service, the next step is comparing Australian providers. Our guide to the best VoIP phone system for small business in Australia covers the top hosted options with pricing and feature comparisons.

For a plain-English comparison of how VoIP stacks up against a traditional phone service in practice, see our guide to VoIP versus traditional phone for Australian businesses.

If after reading this you're still unsure whether to go with a standard SIP setup or a proprietary phone system, or which provider makes sense for your business, we can give you a specific recommendation. Tell us how many staff need phones and what you're currently using. We reply personally, usually within one business day.