Best SIP Trunk Providers for Upgrading a Legacy PBX System


After a year of evaluating over 30 SIP trunk providers, UCaaS platforms, business phone systems, and call center solutions, Nextiva is the top choice for an affordable, easy-to-set-up, and feature-rich option. 

Best SIP Trunk Providers: Our Top Three Recommendations

Nextiva is our number one choice because of its relatively low cost, fast setup, and wide range of features, including fraud mitigation, E911, auto-failover, and more.

Twilio is our runner-up because of its no-contract, pay-as-you-go pricing model and its high degree of scalability for fast-growing, smaller businesses. 

Plivo takes third place because of the vast reach of its SIP trunking services, with over 190 countries available for outbound calling. Plus, if your business only needs SIP trunking with no other services, Plivo has a dedicated SIP trunking product called Zentrunk.

SIP vs. PBX vs. VoIP: Concepts Explained

Before making your own selection, it’s important to review what SIP technology is and how it differs from other similar technologies.

  • SIP stands for Session Initiation Protocol. It’s a specific technology for initiating, operating, and ending communications such as messaging, voice calling, and video calling. SIP is related to VoIP because it forms the foundation that allows VoIP to work in the first place. SIP trunking refers to using SIP technology to connect a business’s PBX to the internet.
  • PBX stands for Private Branch Exchange. A PBX is a system responsible for managing calls to and from a business. While a traditional PBX uses a public switched telephone network (PSTN) to physically connect calls through copper wires, a modern PBX uses SIP and other protocols like IP to route and manage calls.
  • VoIP stands for Voice over Internet Protocol, a broad technology that enables phone calls over the internet. In contrast with PBX, VoIP uses more specific protocols like SIP to do this job. 
  • UCaaS stands for Unified Communications as a Service. It combines text-based messaging, voice calling, and video calling into one easy-to-use application. UCaaS utilizes VoIP and SIP in order to accomplish this.
  • CCaaS stands for Contact Center as a Service, which is a specific type of UCaaS designed for contact centers with high call volumes and complex needs.
  • CPaaS stands for Communications Platform as a Service. It provides APIs for developers to add real-time communication features to their applications without needing to deal with backend infrastructure. Used correctly, it can provide the same benefits of UCaaS platforms with additional customization potential.

Nextiva: The Best SIP Trunk Provider Overall

Most businesses looking for a SIP trunk provider will find that Nextiva meets their needs. It already has over one million total users and over one hundred thousand business clients. 

If you’re looking for more than just SIP trunking, Nextiva is also a full-featured UCaaS platform that combines messaging, audio calls, and video calls into one aesthetic, easy-to-use interface.

What’s So Good About Nextiva?

Nextiva is simultaneously one of the most advanced SIP trunk solutions on the market and one of the most affordable. It offers two flexible pricing options depending on your business’s needs. Metered pricing costs $15 per month and $0.008 per minute of calling, while unmetered pricing costs $25 per month and includes unlimited nationwide calling.

Even though it has many advanced features, getting started with Nextiva’s SIP trunking service is uncomplicated. Your business’s phones can be fully functional in just four easy steps: 

  • Getting a personalized quote
  • Checking for compatibility
  • Porting your number(s)
  • Setting up a PBX connection

You’ll also have a dedicated agent from Nextiva to walk you through every step of the process. The easy setup process means your business will experience minimal downtime as it implements Nextiva’s SIP trunking services.

Nextiva - Start using SIP trunks in four steps

Keep in mind that Nextiva has AI-driven phone services and eight data centers in the United States for cloud redundancy. Plus, with the ability to add additional trunks, channels, and direct inward dialing (DID) features, your business can stay innovative and efficient with its SIP trunking technology. 

If you’re ready to get started with Nextiva, you can get a personalized quote today. For more info, take a look at our full Nextiva review.

Twilio: Best for Small Businesses

Twilio is recognized as one of the best communications companies on the market, however its SIP trunking service caters to a slightly limited audience. In particular, it tends to be best for small businesses and those experiencing fluctuating call volumes. 

Meanwhile, Twilio also offers a host of other communications-related products and solutions, such as SendGrid for mass emailing and marketing, and Twilio Flex for improving customer service and sales engagement numbers. 

What’s So Good About Twilio?

Few SIP trunk providers are more cost-effective than Twilio for small businesses. This is because Twilio markets itself as a fully contract-free, pay-as-you-go SIP trunk provider. Rates for outgoing domestic calls start at $0.0053 per minute. That’s about half a cent for every minute of call time—or $0.32 per hour. If you have a small business with low or fluctuating call volume, you will save money by only paying for the call time you actually use.

Twilio elastic SIP trunking rates

One potential downside to Twilio’s pay-as-you-go pricing structure is that it’s the only option available. Many businesses with high call volumes benefit tremendously from an unmetered, flat-rate SIP trunk plan. Thus, Twilio can only save you money if your calls stay below a certain volume.

Twilio has “Elastic” SIP Trunking, a cloud-based solution for making and receiving calls to anywhere in the world over a broadband internet connection. This easily scales alongside smaller, fast-growing businesses with constantly changing needs. 

You can also manage things independently with Twilio’s self-service trunk, which allows you to take control of the process and upgrade or downgrade the service as needed without relying on anyone else. So, whether your business has three employees or 300, Twilio will adapt to meet your needs.

Twilio’s trunking service makes it super easy to get signed up for free.

Plivo: Best for International Calling

Many businesses need to contact international branches, suppliers, and customers on a regular basis. If that’s the case with you, then Plivo was practically made just for you. It’s a smaller company with fewer overall products, but it has a strong SIP trunking service that can compete with the best. 

What’s So Good About Plivo?

Plivo boasts a vast global reach, with SIP trunking services that can make phone calls to over 190 different countries. Its Points of Presence (PoPs) are located in six countries. 

  • California and Virginia, United States
  • Frankfurt, Germany
  • Mumbai, India
  • Singapore, Singapore
  • Sydney, Australia
  • São Paulo, Brazil

With these locations spread across the globe, Plivo can provide your business with fast, crystal-clear international calling almost anywhere.

Zentrunk quality SIP trunking

Most businesses that make loads of international calls probably already have a phone system in place, which means they may only need to find a specialized SIP trunking solution. This can make Plivo a more attractive choice than a full-on UCaaS platform.

Plivo’s main downside is its initial setup difficulty, which comes at the cost of its many good things, including wide integration capabilities, API access, and extensive customizations. Just keep in mind that if your business lacks a strong technical team, the initial setup may be overly complex and time-consuming. 

Plivo offers free trials upon request.

How Does SIP Trunking Work and Why Is It Necessary?

Here’s more on how SIP trunking works and why it needs to be a part of the business communications conversation.

How to Call with SIP Trunking

  • Starting a call: Whenever you make a call, your phone communicates with your company’s PBX system, which is basically like the internal switchboard for managing calls.
  • Connecting to the internet: The PBX system utilizes SIP technology to convert your voice into digital data packets, which can be sent over the internet instead of clunky, traditional phone lines.
  • Finding the destination: The SIP trunk, which is essentially a virtual phone line, routes call data packets through the internet on a quest to reach the recipient. It finds the recipient by using SIP authentication methods and the number you dialed as an “address.”
  • Reaching the recipient: The recipient’s service provider receives the data packets and converts them back into voice signals.
  • Connecting the call: You can now talk with the recipient via SIP calling, a complex process that happens almost instantaneously, as well as constantly throughout the call.
  • Ending the call: When the call is finished, the SIP protocol handles the disconnection, signaling to end the session and close the phone connection.
  • Why is SIP Trunking Necessary?

    Why not just use a broad UCaaS platform and be done with it? Why would your business ever need to get into such technicalities as SIP trunking? Three reasons:

  • If your business already has an existing PBX infrastructure, SIP trunking can work alongside it instead of replacing it with a full-on UCaaS, saving you time and money.
  • SIP trunking offers much more extensive customization options than a packaged UCaaS service. For example, if your business has hyper-specific phone calling needs or you just prefer to be in total control of your own system, then SIP trunking can easily meet those needs.
  • If your business communication needs are limited to simple voice calling, SIP trunk providers can be much cheaper than UCaaS providers, which usually offer a host of additional, cutting-edge features.
  • What Matters Most When Reviewing SIP Trunking Providers

    If Nextiva, Twilio, and Plivo lack the features you need, you can use these pointers to conduct more SIP trunk provider research. Apart from the more obvious things, there are the five main criteria that we like to consider.

    Codec Compatibility and Optimization

    • What it means: Codec stands for coder-decoder, and it’s what compresses and decompresses the digital data packets sent from device to device. There are many different kinds of codecs—some facilitate super high-quality calls, and others prioritize faster data transfer with some loss. 
    • Why it matters: The types of codecs used by your SIP trunking provider won’t just affect call quality, but also the overall cost of operations for your business. Depending on their quality level and how much bandwidth they need to operate, you may be better off with one over another.
    • What to look for: Look for providers that support a wide range of different codecs. High-quality, uncompressed codecs like G.711 and medium-quality, bandwidth-efficient codecs like G.729 are ones to watch for. Similarly, advanced codecs like Opus adjust to network conditions on the fly, offering the best possible quality in all circumstances.

    Session Border Controller Capabilities

    • What it means: Every time your voice data crosses over from your private network into public internet space, there’s a security risk. Session Border Controllers, or SBCs, are the gatekeepers that monitor and secure your voice data every time it crosses one of those borders.
    • Why it matters: Your SIP trunking will only be as good as its SBCs are, as the security, reliability, and quality of your phone calls all depend on the work done by SBCs.
    • What to look for: Look for providers that have SBCs with high call quality, heavy simultaneous call volume capabilities, robust fraud detection and security protocols, interoperability between different devices and networks, and built-in failover mechanisms.

    E911 Service Integration

    • What it means: E911 just stands for Enhanced 911. E911 services are what ensure that emergency calls get routed immediately to the relevant police station, along with automatic location data from the caller.
    • Why it matters: Emergencies are no joke—and with SIP trunking, calls can come from any internet connection, so the automatic transmission of location data is especially important. E911 is also a legal requirement in many areas of the country.
    • What to look for: A good SIP trunk provider should integrate E911 services and set everything up so that your SIP trunk lines are associated with your business’s actual location. This location data should be customizable for remote employees using the SIP trunking service in other locations. 

    Number Portability Support

    • What it means: Number portability means that businesses can switch to a new SIP trunk provider while keeping their existing phone numbers. For call centers with many numbers listed online for customers, number portability is all but non-negotiable.
    • Why it matters: Even with perfect number portability, switching to a new SIP trunk provider will result in minor hiccups and customer service disruptions. Without number portability, however, the disruptions will be much worse, and your business’s reputation can take a major hit.
    • What to look for: Look for SIP trunk providers that are not only forthcoming about their number portability processes, but also willing to guide you through the entire process to ensure minimal downtime.

    Public Switched Telephone Network Redundancy

    • What it means: Public switched telephone network (PSTN) redundancy is what keeps your phones working when your main internet connection goes down. The process is complicated, but in the event of an internet crash, this redundancy means your phones can hop over to traditional PSTN lines so that calls will still be routed through alternate means and data centers.
    • Why it matters: Your internet will inevitably go down at some point—and it will probably feel like it happened during the most important call of the year. Hence, PSTN redundancy may be the only thing standing between your business and a massive loss of customer or investor trust.
    • What to look for: At a minimum, choose a SIP trunk provider that advertises automatic failover mechanisms. Better yet, test and confirm any purported redundancy plans from your SIP trunk provider before you perform the full company-wide rollout.

    How To Get Started With a SIP Trunk Provider

    Consider the following steps for determining which provider is right for you and rolling things out the right way. 

  • Identify your needs: What do you want to accomplish with your SIP trunk provider? How much call volume do you expect? What pricing structure makes the most sense?
  • Create a shortlist: Narrow down the top providers into a concise list.
  • Research providers: Conduct some deep research into each provider’s features, pricing, and compatibility with your existing system.
  • Schedule calls and demos: Contact the providers on your list to arrange calls and demos so you can see their services in action. Come prepared to ask questions.
  • Trial phase: If available, start a free trial with your top providers, using a small testing team to note the pros and cons of each.
  • Evaluate: Assess each option based on the findings of your team. Take the feedback seriously, especially when it comes from the people who will be using the system every day. 
  • Strategic rollout: Consider what will happen if you stop operations to change everything all at once. Make sure you have enough employees who are familiar with the new system to keep operations at full speed when the change occurs—and prepare for the worst just in case it happens. 
  • Recap

    SIP trunking is a complex phone service that serves specific communication needs. 

    For some businesses, SIP trunking is a necessity, so understanding it on a deeper level and finding the right provider can make a difference in your future business success.

    For most businesses, options like Nextiva, Twilio, and Plivo can take care of all their SIP trunking needs. Of the three, Nextiva is the best overall.

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