VoIP is the general technology for carrying voice over IP networks; a SIP trunk is one specific VoIP service that connects a whole phone system to the telephone network using the SIP protocol. Every SIP trunk is VoIP, but VoIP also includes hosted phone systems, softphone apps and wholesale carrier routes.
What is the difference between SIP and VoIP?
VoIP (Voice over Internet Protocol) describes the whole idea: voice is turned into data packets and sent over an IP network instead of a circuit-switched phone line. SIP (Session Initiation Protocol, RFC 3261) is one protocol used inside VoIP to set up, change and end calls. Other VoIP signalling protocols exist, such as H.323 (still found on older carrier equipment), IAX2 (Asterisk) and the proprietary protocols of apps like WhatsApp. SIP is the dominant one between businesses and carriers.
So "SIP vs VoIP" compares a part with the whole. A better comparison is a SIP trunk against the other ways a business can use VoIP.
SIP trunking vs VoIP: what's the difference in practice?
| SIP trunk | Hosted VoIP (cloud phone system) | Consumer VoIP apps | |
|---|---|---|---|
| What you buy | A connection for your own PBX or platform | A complete phone system run by the provider | An app account |
| Who runs the PBX | You | The provider | No PBX |
| Priced by | Channels and/or minutes | Users or seats per month | Free or per minute to phone numbers |
| Calls to phone numbers | Yes, any destination the provider covers | Yes, usually with bundles | Limited |
| Typical buyer | Businesses with a PBX, call centers, CPaaS, carriers | Small and mid-size offices | Individuals |
A full explanation of how a trunk works is in what is SIP trunking. The choice between running your own PBX with a trunk and buying a hosted system is covered in SIP trunk vs hosted PBX.
Is a SIP trunk VoIP?
Yes. A SIP trunk carries calls as IP packets: SIP for signalling and RTP for audio. The difference from a basic VoIP line is scope. A VoIP line usually serves one user or device, while a trunk serves a whole system with many channels at once, plus a range of phone numbers (DIDs) routed to it. See what a DID number is.
SIP vs VoIP vs PBX: how do they fit together?
- PBX: the phone system that handles extensions, queues, IVR and call routing inside the company. It can be on-premise (for example Asterisk, FreePBX or 3CX) or hosted.
- SIP trunk: the link between that PBX and the outside telephone network.
- VoIP: the technology both of them use.
Before SIP trunks, the same link was a physical line such as an ISDN PRI. Our page on SIP trunk vs PRI compares the two. A session border controller often sits between the PBX and the trunk for security and interoperability.
Which one do you need?
- You already have a PBX or contact center platform: buy a SIP trunk. You keep your system and choose the carrier separately.
- You have no PBX and few users: a hosted VoIP service is simpler, because the provider runs everything.
- You send high volumes to many countries (call center, CPaaS, reseller): you need wholesale VoIP termination routes over SIP, priced per destination, often from several carriers at once.
Wholesale routes are SIP trunks too, but bought differently: per destination rate deck, with a stated CLI type, channel and CPS limits, and a billing increment. See SIP trunk channels and CPS for sizing.
Getting wholesale SIP routes
If you run your own platform and need routes to specific countries, VoIPMatcher sources them from its carriers and manages them for you; your company data is never shared or sold. Read about our VoIP termination service, then request a SIP trunk route.
Frequently asked questions
Is SIP better than VoIP?
The question compares a part with the whole. SIP is a protocol used within VoIP, so it is not better or worse than VoIP. What you can compare is a SIP trunk against a hosted VoIP phone system: the trunk gives more control and usually lower call costs, while the hosted system needs less technical work.
Can I use a SIP trunk without the internet?
A SIP trunk needs an IP connection, but not necessarily the public internet. Many carriers and large companies connect over private links, MPLS or dedicated cross-connects in data centers, which avoids internet congestion and improves security. Small businesses usually run trunks over their normal broadband connection with QoS enabled.
Is SIP the same as a VoIP phone number?
No. SIP is the signalling protocol, and a phone number is an address in the telephone numbering plan. A VoIP phone number, often called a DID, is a number that a provider routes to your SIP trunk or VoIP account, so calls to it reach your system over the internet.
Do SIP trunks work with Microsoft Teams?
Yes. Microsoft Teams Direct Routing connects Teams to a SIP trunk through a certified session border controller, so you can use your own carrier for calls to phone numbers. Operator Connect is the alternative, where a participating operator provides the connection and you manage it from the Teams admin center.
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