SIP trunk for your company – a complete guide

SIP trunking is a method for communicating over the internet that grows in popularity. SIP trunking allows your fixed phones as well as softphones to connect to the fixed telephone network to make a call. SIP trunking uses IP to connect a phone call to the fixed telephone network (PSTN). That is instead of the traditional course of action with PRI or analogue phone lines. Hence, SIP trunking connects your internet provider to your PBX.


Why is this so favourably, and something more companies choose to invest in? For starters, it is a trustworthy solution for the future since we will definitely continue to communicate online. Also, more and more businesses transfer their activity to the cloud. It is also a way to reduce company costs for telephony and something that will increase flexibility within the company.

In this guide, you’ll get all the information you need to be able to decide if SIP trunking is something for you. You will also learn everything about communicating over the internet. Sounds good? Let’s go!

The history of SIP

To understand SIP, we need to return to life before the internet. Then, you used regular telephones to make calls over the analogue network PSTN (Public Switched Telephone Network). A network consisting of copper wires (PRI), where a physical connection between two points was required for a call to work. As the service was further developed, companies could buy a package, a so-called trunk, from their supplier. The trunk then consisted of many telephone lines.

Since the 1980s, copper lines have used ISDN to connect to the internet, and trunking has evolved into IP trunking. The main difference between traditional trunks and IP trunks is that instead of copper wires, you use IP connections over the internet.

The world’s first VoIP call

In the late 1970s, VoIP was developed using several different protocols. The first VoIP call outside of the analogue copper wires then went over the IP network. Then, an NVP (Network Voice Protocol) was used over the Arpanet (the predecessor of the internet). The first VoIP software to be installed on home computers came in 1995. In 2003 the perhaps most well-known alternative today, Skype, was introduced to the market.

SIP gets introduced

SIP was developed in 1996 and made it possible to include video and chat, besides the voice. It has become the most used protocol for voice calls that is compatible with IP based PBXs and other VoIP products. Many companies started using it early as they liked the fact that they could make calls over the internet. They just needed one network for all media and could exclude the physical telephone cables.

In the early 2000s, cables and DSL connections for internet services were used to a greater extent (instead of the analogue PSTN lines). That meant faster internet, which in return resulted in VoIP technology being used in a better way. When VoIP became more popular, you needed SIP trunking to be able to call with several techniques. Without SIP trunking, VoIP had only meant making voice calls in-house. Then you would still need to use the copper wires to make calls outside of the office.

How SIP trunking works

One thing is assured, and that is that we will transfer entirely to communicating over the internet. We have come a long way in Sweden. Most companies here have phased out their stationary PBXs and started using cloud-based solutions. But you can communicate over the internet in several ways. One of the most popular approaches is SIP trunking.

SIP trunks are virtual phone lines that use SIP protocols to make voice calls (VoIP). With SIP, suppliers can connect to your PBX, and all your phone numbers can be connected to the SIP trunk. A SIP trunk can have an unlimited amount of lines, so you never have to worry about increased costs if you add more lines or remove existing ones!

What do you need to be able to use a SIP trunk? 

An internet subscription and SIP compatible PBX is all you need to use a SIP trunk. The speed of your internet connection needs to be fast, but today that is usually not a problem since most suppliers meet the requirements.

How do you know if your PBX is SIP compatible? 

Most new PBXs are compatible with SIP. Older PBXs are developed for the copper network, and those might need an upgrade, or you have to buy a new one. It is possible to invest in a gateway that allows the traffic on your old PBX to be routed through the internet instead. Although older, fixed PBXs are usually more expensive and harder to maintain. To review other options is, thus, a good idea and investment for the future.

Pros and cons of SIP trunking

Decreased costs and increased flexibility

Since all calls are routed over the internet, you don’t have to pay per minute or call. There will thus be a lower subscription and traffic cost. Since this is a solution available to everyone connected to the company, it doesn’t matter if your employees work from home. Their calls will also be free of charge. You will also reduce costs for installation, configuration, maintenance, hardware, among other things.

Since SIP trunks aren’t physically bound to a specific place, you don’t have to change numbers when you move into a new office either. It is a scalable solution, so you can reduce the number of lines if necessary and scale up without any extra charge. You can also add new users quickly.

Another positive aspect is that transferring to SIP trunking won’t affect the company or employees in their daily work. No one will notice the transfer. The only clear difference is that you call over the internet instead of the copper wires.

Disadvantages of SIP trunking

If you have a fixed PBX and want to install a new solution, it will initially demand an investment in new equipment.

It is seldom a big problem if the internet connection stops working, but if the internet is down, it won’t be possible to make a call. Then, of course, there is the option to use your mobile phone instead.

Finally, it is also worth noting that since SIP trunks are exposed to the internet, so you need well-functioning network security. SIP trunking does not in itself lead to an increased risk, but you need appropriate security measures in place.

Is a SIP trunk something your company needs?

Must I have a SIP-trunk to be able to call over the internet?

No. There are other available solutions besides the traditional PBXs and SIP trunking – like customised UCaaS solutions. UCaaS (Unified Communications as a Service) is a name for cloud-based communication solutions. It is a way of gathering your company’s communication in one platform. You can have your PBX, mobile telephony, and chat in one app.

Who is SIP-trunking suitable for?

SIP-trunking is a smart solution for larger companies that use many phone numbers. It is also suitable for companies that have an existing PBX they don’t want to get rid of. Mainly it’s about looking at your needs and demands on telephony and communication. If you only make voice calls and don’t require other functionalities, SIP trunking can be a great solution to cut costs and increase flexibility.

Common questions and answers about SIP trunking

How long does it take to install a SIP trunk?

If you meet the requirements, with a fast enough internet connection and an IP compatible PBX, implementation can be done in a few minutes. You only need to determine what numbers you want to use and where you want to route the calls.

There can be a need for configuring your PBX so that it communicates with the SIP trunk supplier’s PBX. If so, you might need to do a quick reprogramming.

How are SIP trunk solutions different from each other?

The solutions do not really differ at all. SIP trunk solutions are, in general, simple and stripped of advanced functionalities. Mainly it’s about being able to connect calls through the fixed network with the equipment you’ve got. It is a simple solution if you want telephony at a low cost, without any extras.

Make a price comparison and review the offers of different suppliers. Ask them what will happen if the internet connection is down and what their availability of services looks like.

Is SIP-trunking safe?

Some feel concerned about SIP trunking and that calling over the internet won’t be as safe as calling over the fixed telephone network. Some fear that SIP will open up to vulnerabilities in the network or that it will be easier for unauthorised persons to listen in on calls.

Yet, SIP trunking does not imply any extra vulnerability for network security. It is only a protocol that ensures that you can send and receive information. It functions as a controlled gateway to PSTN, the analogue telephone network. SIP trunking has nothing to do with your network security. However, SIP trunks are exposed to the internet, so your network security must be stable.

SIP trunking, thus, becomes what you make of it and how you use it. A regular phone can also be a security risk. If you choose a supplier that knows how to set it up, it is very secure.

Make sure your network is safe

Make sure your software is up to date to reduce the risk of security issues. Update everything from your router to your PBX. Use complex passwords that you change regularly, and secure your PBX with firewalls.

Ask your supplier if they use their network or someone else’s. Some suppliers sell SIP trunks from other suppliers. You want to pick someone that uses their network and, thereby, has full control over their service.

Will the voice quality of calls suffer if you use SIP? 

In short: no, on the contrary. Voice quality depends on which parameters the operator uses and which phone you have. Many providers use HD Voice, which provides a speech quality superior to the old telephone network.

Alternatives to SIP trunking

Is SIP-trunking the best telephony solution? 

Calling over the internet is the most future-proof solution, for now, at least. Using VoIP technology is suitable for most companies and industries regardless of how much you call and where your office is. You need to take a look at your current need for telephony and what you will need in the future.

If you want to keep your PBX and are looking for a simple solution

Have you recently invested in a cloud-based PBX, or do you have a stationary PBX that you want to keep? Then you can integrate it with SIP. A new cloud-based PBX is probably already IP compatible, but you might need to upgrade an older PBX before implementation.

Telavox’s SIP trunking solution allows you to keep your existing PBX, but you use us as an operator. That means we connect your calls and handle integration with a SIP trunk, which allows you to call over the internet. For this to work, a strong internet connection is required.

Telavox’s SIP solution in 5 words

1. Cost-effective

Your company can lower costs. You no longer need physical phone lines that aren’t flexible and expensive to maintain. International calls will also be much cheaper.

2. Global

Telavox uses Voxbone’s global SIP trunking solution, which allows us to offer numbers in over 65 countries. Also, many Telavox customers use their Nordic accounts for their worldwide contact centers.

3. Flexible

Adjust after what your company needs right now by scaling up or down. With physical phone lines, it was a time-consuming and complex task to increase the number of phone lines. Modern VoIP solutions with SIP trunking make these kinds of changes almost immediately.

4. Future-proof

SIP trunking is a solution for the future. The old network consisting of copper wires is being discontinued in large parts of the world. With SIP trunking, you can be sure that your voice calls always reach the other part, even in areas where there are no physical networks.

5. Integration-friendly

Integrate with other telephony environments via SIP. Telavox supports Mitel, Avaya, Aastra, and LG-Ericsson’s local suppliers. Telavox also provides several integrations with CRM systems and Microsoft Teams.


A complete, user-friendly UCaaS solution

If you want to take it to the next level, you should invest in a solution optimised for the future. A solution that ensures even better communication both within and outside the company. For this, there are several options.

Telavox has always aimed at the future. When we started our company, it was to develop a better way for companies to communicate and move company communication to the cloud. We are different from many other UCaaS suppliers since we have developed and own everything ourselves. We have worked with telephony over the internet since the very beginning. That has allowed us to refine and improve our solution continuously.

Our communication platform comes complete with PBX, telephony, and mobile telephony. You can use whatever unit you like to communicate the way you prefer – you’ll still get the same experience. Here you can read more about all the advantages of our solution.

Appendix: The-little-call-online-dictionary

Audio Codec

Codec is short for encoder/decoder where you digitally compress and decompress sound. It is a process where you reduce the file size to achieve a faster transfer online. When it refers to calls over the internet, it means that the voice (the audio signal) is being digitally compressed. When the audio signal reaches the final destination, it is decompressed so it can be played in full quality. That is how VoIP is made possible.

DID (Direct Inward Dial)

SIP trunking uses DID (Direct Inward Dial). That means everyone at the office can have their own SIP line. To be able to use DID, you need to use ISDN or another digital connection. DID is a function that gives all employees their own phone numbers without having to use a dedicated telephone line for this.

DSL (Digital Subscriber Line)

Another method for connecting to the internet by using telephone lines. Like ISDN, speech and data can be transferred simultaneously.

IDSN (Integrated Services Digital Network)

A common method for connecting to the internet over regular phone lines. A technology developed during the 1980s. Since the network is digital, you can use several units at the same time, like telephones and computers.

IP (Internet Protocol)

IP telephony means you call over the internet instead of the traditional fixed telephone network. IP is the communication protocol that is used to send information over the internet.

PSTN (Public Switched Telephone Network)

The analogue traditional telephone network, consisting of copper wires.

QoS (Quality of Service)

QoS is a router setting asking the network to prioritise voice calls to avoid disturbances and lost quality. With the QoS setting, you always keep the sound quality – even when doing data-consuming activities such as streaming video or downloading large files.

SIP (Session Initiated Protocol)

SIP is the protocol being used to send voice data over the internet. A SIP trunk enables online calls, i.e., streamed calls instead of the traditional telephony over the fixed network.


Either hard- or software phones that use VoIP for calls. Another name for VoIP phones or softphones. 


A softphone is software you install on your computer or tablet to be able to use the unit as a regular phone. It is most often used in conjunction with VoIP to make calls over the internet.

UCaaS (Unified Communications as a Service)

UCaaS means to subscribe to (most commonly) cloud-based solutions for Unified Communications. For example, a basic version of UCaaS can gather the company’s telephony, chat, PBX, email, and video calls in one platform.

VoIP (Voice over Internet Protocol)

A technology or concept for voice calls over the internet. It is sometimes called IP telephony, broadband telephony, and internet telephony.

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