SIP Trunk Providers

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Solgari is a cloud-based contact center and communication solution for small, midsize and large businesses. It caters to financial services, FinTech, e-commerce, retail, logistics, recruitment and government. Primary features incl...Read more about Solgari

5.00 (1 reviews)


Nextiva is a platform that brings communications together with business applications, intelligence, and automation. This helps businesses communicate and build deeper connections with their customers. The platform brings all ...Read more about Nextiva

4.10 (205 reviews)

28 recommendations

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Comm-unity by NetFortris (formerly Fonality) is a cloud-based communication and collaboration business phone system that caters to all business sizes. Comm-unity scales easily as your business grows, always works when you need it,...Read more about Comm-unity

3.37 (15 reviews)


Answer360 is a cloud-based VoIP solution designed for small and midsize businesses. The solution offers call routing, video conferencing, SIP trunking and other call center functionalities. Answer360 offers hosted VoIP phone ...Read more about Answer360

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AVOXI Genius is a cloud-based call center solution that helps small to large enterprises streamline customer service operations and manage business communications. It comes with a centralized dashboard, which enables users to trac...Read more about AVOXI

4.76 (50 reviews)

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Convoso’s all-in-one contact center platform generates and converts leads faster using multiple communication channels. The cloud-based solution offers multiple dialing modes (predictive/power/preview) along with two-way texting, ...Read more about Convoso

4.59 (58 reviews)

1 recommendations

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Five9 is an all-in-one cloud contact center solution for inbound, outbound, blended and omnichannel contact centers world-wide. Powered by Practical AI, Five9 enables agents to provide customer experiences across phone, emai...Read more about Five9

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RingCentral MVP

RingCentral MVP is a cloud-based business communications solution that offers tools for Messaging, Video and Phone. Core features of the solution include conferencing, auto-recording and unlimited long-distance and local calling. ...Read more about RingCentral MVP

4.22 (1017 reviews)

35 recommendations

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Bright Pattern

Bright Pattern is a cloud-based contact center software solution which helps businesses manage multichannel service including inbound and outbound voice, email, chat, and social media. Bright Pattern scales from 5 to 10,000 concur...Read more about Bright Pattern

4.73 (98 reviews)

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Vonage Business Communications

Vonage Business Solutions is a cloud-based communications solution suitable for small and midsize companies. The solution offers a business phone system that enables businesses to connect their VoIP phone system to internet-enable...Read more about Vonage Business Communications

4.06 (263 reviews)

6 recommendations

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MiVoice Business

Mitel MiVoice Business offers a range of unified communications (UC) platforms designed for both small business and large enterprise needs. MiVoice offers virtualization options and supports both cloud-based and on-premise deploym...Read more about MiVoice Business

4.33 (3 reviews)

XMission Hosted PBX

XMission is a cloud-based hosted PBX solution that offers a set of business services which include web hosting, unified email and collaboration. XMission allows users to retrieve a voicemail from a specific email address. The...Read more about XMission Hosted PBX

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TelePacific Hosted PBX

TelePacific's UCx is a hybrid phone solution that offers businesses PBX and business communication features such as auto-attendant, voice and video calling and more. It also offers SIP trunking, PRI/CAS and analog services for bus...Read more about TelePacific Hosted PBX

5.00 (1 reviews)

BroadVoice Cloud PBX

BroadVoice b-Hive helps call and collaborate from anywhere with a single cloud communication solution that unifies business phones, video conferencing, texting and collaboration under a single phone number. Untether your team fro...Read more about BroadVoice Cloud PBX

4.55 (29 reviews)

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OnSIP Hosted OnSIP Hosted VoIP by Junction Networks is a cloud-based phone solution that offers businesses across various industry verticals PBX feature such as auto attendants and voicemail-to-email. Unified communications (...Read more about OnSIP

4.67 (9 reviews)


AireSpring AirePBX is a cloud-based phone system that provides end-to-end network solution for businesses to make and receive calls. AireSpring offers SIP trunking to users looking for a single-provider VoIP solution. AireSpr...Read more about AirePBX

5.00 (1 reviews)


VirtualPBX is a cloud-based phone solution that caters to all-sized businesses. VirtualPBX enables companies to streamline and improve communications with features such as unlimited minutes, video conferencing, business SMS, auto-...Read more about VirtualPBX

4.85 (23 reviews)

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FortiVoice is Fortinet's on-premise business VoIP solution that caters to small and midsize businesses across various industry verticals. Features include voicemail, auto attendants, dial-by-name directory, ring groups and more. ...Read more about FortiVoice

5.00 (2 reviews)

VoiceMaxx CE

VoiceMaxx CE (Cisco Edition) by West IP Communications is a cloud-based enterprise PBX solution. Key features include inbound and outbound calling capability, call control functionalities, personal conferencing and 'Mobile Connect...Read more about VoiceMaxx CE

3.00 (1 reviews)

Mobex Hosted PBX

Mobex is a cloud-based business VoIP solution that provides bundled PBX and SIP trunking services to small businesses across various industry verticals. Hosted PBX service multiple PBX features and applications, such as ring ...Read more about Mobex Hosted PBX

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Buyers Guide

Last Updated: November 16, 2022

SIP trunking is a network service that allows businesses to connect VoIP phone systems to the traditional phone network. While this service is generally included with “per-user” licenses for cloud-based phone systems, if you have an on-premise system you’ll most likely need a SIP provider to connect calls with it.

We’ll explain what SIP trunking is, why you need it, and the primary considerations that you should factor in when deciding on a provider.

Here's what we'll cover:

What Is the Session Initiation Protocol (SIP)?
What Is a SIP Trunk
Benefits of SIP Trunking
Features of SIP Trunking Service
Important Considerations for Buyers

What Is the Session Initiation Protocol (SIP)?

Imagine the Internet as a vast network of roads and highways. On it are many types of vehicles, delivering various-sized packages (or packets, to use the technical term) containing a variety of information at a wide range of speeds. Most Internet users only ever see the contents of the vehicles traveling on the roads.

But like real roadways, the Internet has many layers below the surface. These lower layers support—and determine the quality of—the layers above them. Each layer has its own specific set of languages used to communicate within that layer. These languages are called “protocols.”

One of the lowest layers supporting the Internet is called the link layer. Within the link layer, link layer protocols organize groups of local connections into large networks. At the top, just under the surface, is the application layer. The application layer determines the quality of the “road surface” directly above it. SIP is a protocol that operates within the application layer.

Different application layer protocols are used to create different surfaces. The Internet has a wide variety of road surfaces, some favoring certain types of traffic over others: Compare a heavily loaded truck slowly climbing the rough road surface of a hill to a sports car zipping down smooth concrete. Some surfaces work better for certain purposes.

VoIP—phone conversations over the Internet—are one very particular type of traffic. They require audio to be delivered consistently with minimal delay. SIP is an application layer protocol designed to provide a very certain type of road surface for this special traffic. SIP initiates the sessions (or connections) that prepare the network to best meet the specific needs of a real-time audio connection over the Internet. 

We offer a fuller explanation in our article on the SIP protocol.

What Is a SIP Trunk?

We’ve mentioned that SIP trunking is a network service. It’s necessary because VoIP calls travel over the internet rather than the traditional phone network. This means that you need some way to connect calls between the internet and the traditional phone network, as otherwise you’d only be able to call other users with VoIP.

SIP trunking is the solution to this problem.

A SIP trunk isn’t a phone “line.” Instead, you connect to your SIP provider’s network using your internet connection. Your SIP provider utilizes specialized technologies to create a bridge between the internet and the traditional phone network, thereby connecting calls between these networks.

In some cases, you can get SIP trunking from the same company that provides your internet service, but in other cases you may need to use separate providers for SIP trunking service and internet service.

If you don’t have SIP trunking, you won’t be able to do much with a business VoIP phone system aside from admiring the server hardware. And while the traditional phone network is dying in the United States, it’s alive and well across the globe, so the need for SIP trunking isn’t going to disappear anytime soon.

Benefits of SIP Trunking

SIP trunking can cut costs in the following ways:

Lower trunking costs. Combined voice and data connections have traditionally been provided by telecoms in the form of Integrated Services Digital Network (ISDN) lines, also known as trunks. ISDN trunks come with fixed quantities of lines per trunk (for example, T1 trunks have 23 lines each). If a business needs even one additional line, it must purchase another entire trunk—meaning businesses often pay for unused capacity. SIP trunks are comprised of bandwidth, a flexible commodity, and their capacity can be increased on the fly.

Lower equipment expenses. Offices without SIP trunks use media gateways to translate between the analog PSTN and the office’s internal digital traffic. Offices using SIP trunks don’t need this expensive piece of equipment because their traffic bypasses the PSTN. A SIP trunk also makes it more practical for an office to use a cloud-based phone system rather than purchasing and maintaining an in-office hardware version.

Lower calling charges. Traditionally, and under many existing calling plans, charges are calculated based on the physical length of the PSTN line required to complete a call. Calls made via SIP trunks bypass most of the PSTN and so avoid many long-distance charges.

SIP providers also frequently offer better rates on international calls than traditional phone service providers, and most importantly, intra-office calls and calls between branch offices are frequently free when connected via SIP trunking.

SIP trunking also has a number of technological advantages:

More communications options. A SIP trunk extends, in a virtual sense, an office’s internal network to the outside world—letting remote offices, mobile employees and customers worldwide interact as if they were in the same building. Click-to-call website options for customers, application sharing and simple call transferring for work-at-home or abroad employees, for example, can all be done more easily with SIP trunks.

Meanwhile, SIP client apps can facilitate communication via a mobile device over an Internet connection, with capabilities such as voicemail, SMS messaging and more.

Features of SIP Trunking Service

The following table shows some common features of SIP trunking service:

Bursting Traditionally, if you needed more calling capacity on your phone lines, your provider took a month or longer to deliver it. SIP providers, on the other hand, can scale capacity up and down in as little as 24 hours, a vital cost-saving feature for businesses with fluctuating call volume.
Port sharing If you have multiple sites, and one site maxes out its number of simultaneous calls, you can connect calls via open ports at one of your other sites. Again, this is a vital cost-saver for call centers.
Disaster recovery In case of a service outage at one of your sites, your SIP provider can forward calls made to critical phone numbers.
911 and E.911 support Your SIP provider can support 911 calls by providing location information with the call. Without E.911 support, VoIP isn’t compatible with emergency services.
MPLS support Multi-protocol label switching is a networking technology that allows information to be routed within a network using path labels rather than the network protocols we discussed above. This offers performance, reliability and security benefits, and some businesses prefer to have SIP trunks delivered over MPLS. You’ll need to make sure your provider offers both MPLS and SIP trunking services, however.

Important Considerations for Buyers

Phone system deployment type. Whether you have an on-premise or cloud-based system is the most important factor affecting your approach to SIP trunking. Businesses with cloud systems may not even need a separate SIP provider.

In most cases, SIP trunking is included with “unlimited” user licenses for cloud systems. The vendor generally doesn’t even mention that SIP trunking is included, given the complex nature of the service. Other cloud vendors provide “metered” SIP trunking - i.e., SIP trunking service priced using per-minute rates. If you have an on-premise phone system, however, you’ll need to search for a SIP provider, as generally vendors of on-premise systems don’t offer SIP trunking.

Phone system brand. Different phone system vendors have implemented the SIP protocol in their systems in different ways. This means that not all SIP providers will be compatible with your specific brand of phone system. Check with your phone system vendor, as many list the SIP providers that their systems support. You also need to ask your SIP provider about support for specific features and devices such as FAX machines.

Connection type. A SIP trunk can be provided over most any high-speed Internet connection. The cheapest option uses an existing broadband Internet connection from a standard Internet service provider (ISP), and simply has the ITSP service share it. Call quality and capacity may be reduced because both data and voice are sharing the connection. A more expensive—but better—option is to lease a line from an ITSP and dedicate it solely to your SIP traffic. Giving your SIP traffic its own line helps improve call quality and reliability. Not all SIP providers offer internet service, but many partner with ISPs.

Quality of service and service level agreements. Quality of Service (QoS) and Service Level Agreements (SLAs) are common components of the contracts businesses sign with their ITSP. The QoS agreement defines (in technical terms regarding IP traffic’s delay, jitter and packet loss) the acceptable average quality of a voice call. The SLA, on the other hand, describes exactly how much "downtime" a service provider is allowed, what constitutes downtime and how quickly network issues must be resolved.

Trial period. ITSPs recognize that it can be difficult for a business to commit to a new phone system without experiencing it firsthand. For this reason, many now offer full or limited trial periods. The trials can be adopted on a small scale to make sure everything is functioning as expected before making the switch. Make sure to test any devices such as FAX machines that are connected to the phone network as well as the actual features of your phones.

911 dialing. The FCC has mandated that all “interconnected” VoIP services provide functionality to connect 911 calls to the appropriate local emergency services authority. But not all ITSPs fall under this mandate. If a business plans to eliminate their PSTN service entirely, then this needs to be considered. Maintaining a single PSTN line for emergencies is a viable option.

Firewall and security. If not properly managed, SIP trunks can expose an office network to external privacy and security threats. Traditionally, offices have used standard firewalls to keep out unwanted IP traffic, but SIP traffic does not always travel smoothly through firewalls. Other security options, like Virtual Private Networks (VPNs) and session border controllers, are increasingly common.