What is an SIP Trunk Service? How is it Different from VoIP?

Posted on: 2019-04-04 | Categories: SIP Trunking

If your business relies on the good old PSTN, it’s time to sit up and notice the changes in the phone industry. Phone companies all over the world are all set to phase out ISDN lines over the next few years. Why? Because no one uses them anymore. Most businesses are giving up their ISDN lines.

What are companies doing for voice calls then? Some of them use VoIP while others are switching to SIP trunks. The adoption rate for SIP trunk service has skyrocketed for a number of reasons. Perhaps the biggest one is the potential to save money. If you can get advanced features at a lower rate than your current service, wouldn’t you switch too?

What Are SIP Trunks?

If you’ve considered SIP trunking in the past but couldn’t understand how it all worked, you’re at the right place. Let’s take a look at what exactly a SIP trunk service does for a business.

In a nutshell, SIP trunks are a way for business phone systems to make calls over the internet instead of a traditional phone line. Functionally, SIP trunks are similar to the ISDN PR1 or T1 lines you already know. But here the similarities end.

While ISDN lines are physical wires, SIP trunks are entirely virtual. There’s nothing for the operator to install or for you to maintain. Everything works over your existing internet connection. As long as you have high-speed internet access and enough bandwidth, you can make and receive calls.

What is a SIP Trunk Service?

SIP trunks services are provided by an ITSP (Internet Telephony Service Provider). They’re similar to phone companies, except they give your business a dial tone over the internet. There are other important distinctions as well. For instance, you can use any SIP trunk service with any compatible IP-PBX system. Even if your on-premise system isn’t IP-compatible, you can make it work with a VoIP gateway.

SIP trunks typically cost much less than the equivalent analog trunk. Companies may see a reduction of up to 50% on their monthly phone bills! Calls between your employees – regardless of location – are free with SIP trunks. Long-distance calls are also less expensive. Of course, your actual savings will vary according to the situation.

ISDN lines come in bundles of 23, no more no less. You can’t just buy the exact number of lines you need. If you need only 30 lines, you have to get 46. There is no middle ground. But with SIP trunks, you can get as many as you need. A small office with two dozen employees can get by with just four or five SIP trunks. Need more? Add as many as you want when you need them, not a moment before.

Selecting a SIP Trunk Service Provider

Once you’ve decided on using SIP trunks, the next step is to select the provider. There are many companies on the market offering SIP trunk services at multiple price points. You can get metered and unmetered trunks depending on your call volume. Some providers offer additional features for an extra fee. Others bundle them into the base plan.

As such, comparing SIP trunk service between different providers becomes difficult. Here’s what you need to consider before choosing one provider over another:

Network and Service

Does the provider own their network? There are many resellers who will sell you rebranded SIP trunks but they’re not in control of the network. When a problem crops up, your vendor has to depend on another company to solve it for you. It means you cannot rely on your phones to work when you need them to.


SIP trunks connect you to the vendor over the Internet. This means they have to be secured against hackers, criminals, and other fraudulent entities. Even if you do everything by the book and follow security best practices, you can get hacked through the provider if they aren’t careful.

Customer Service

It is easy to overlook tech support and customer service when trying to choose a provider. After all, there are costs and features to consider. But sooner or later you will run into problems with the phone service. And then you’ll wish you had gone with the provider who is responsive and proactive enough to solve your problems.


You want to use SIP trunks to save on costs. But that doesn’t mean you should skimp on quality. Make sure the provider offers you competitive rates for the features you are interested in. Don’t just go with the cheapest quote, be prepared to pay for business class service.

Whether or not SIP trunks are the best choice for your business depends on many factors. But between hosted VoIP and SIP trunking, there’s no reason to stick with the PSTN. Why should you lose out on functionality while paying more than your competitors?