Finding software can be overwhelming. Software Advice has helped thousands of businesses choose the right SIP trunking software so they can reduce their phone bills and connect calls.

Showing 1-20 of 82 products

Nextiva Office

Nextiva is a business-focused VoIP phone system serving small businesses and enterprises. The Nextiva VoIP service provides users with a complete phone, chat, texting, and fax solution. Customers get more than phone service. They... Read more

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Recent recommendations: 71 recommendations

Platforms: MacWinLinux
Deployments: Cloud
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net2phone

net2phone’s cloud PBX VoIP phone solution enables businesses to communicate in a variety of methods, whether voice, texting, messaging or web chat, over an array of devices, in the office and on the go. The net2phone solution features... Read more

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Recent recommendations: 9 recommendations

Platforms: MacWinLinux
Deployments: Cloud
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Twilio Voice API

Twilio's Voice API is a fully programmable VoIP system that helps companies make, manage and route calls to a browser, app, phone and more. Key features include call monitoring, call transcripts, call routing, PBX, auto dialer / predictive... Read more

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Recent recommendations: 7 recommendations

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Deployments: Cloud
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PGi UCx Unified Communications

UCx, a new generation Unified Communications as a Service (UCaaS) solution, helps customers create connections with their employees, customers and shareholders. UCx provides a rich feature set including enterprise voice, a cloud-based... Read more

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Recent recommendations: 7 recommendations

Platforms: MacWinLinux
Deployments: Cloud
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Vonix Flex VoIP

Vonix flex is a business VoIP solution that provides hands-on support and reliable service with all business phone plans for small and medium businesses across the U.S. This cloud-based communication platform helps businesses connect... Read more

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Recent recommendations: 3 recommendations

Platforms: MacWinLinux
Deployments: CloudOn premise
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ClickITVoip

ClickITVoip is a cloud-based communication management system designed to help businesses engage with clients and employees via text messages, calls, video conferences and more. The platform includes an automated attendant, which automatically... Read more

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Recent recommendations: 3 recommendations

Platforms: MacWinLinux
Deployments: Cloud
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Versature

Versature’s cloud-based business VoIP services provide Canadian companies with unified communications and call analytics solutions to help manage their business operations. Versature’s key features include auto attendants, click-to-dial,... Read more

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Recent recommendations: 2 recommendations

Platforms: MacWinLinux
Deployments: Cloud
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NICE inContact Hosted Call Center

NICE inContact is a SaaS-based call center software that helps businesses to maximizes the quality of leads and minimizes the cost of client interaction. The solution comprises of many features required to process inbound support requests... Read more

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Recent recommendations: 1 recommendations

Platforms: MacWinLinux
Deployments: CloudOn premise
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Voximplant Platform

Voximplant is a full-featured cloud communications platform as a service that enables organizations in industries such as banking, retail, classifieds and logistics to create and deliver innovative customer communications using voice,... Read more

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Recent recommendations: 1 recommendations

Platforms: MacWinLinux
Deployments: Cloud
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Five9 Cloud Contact Center

Five9, an early adopter of SIP trunking, combines a wide range of network connectivity options including SIP trunks and gateways with one of the industry's most robust selection of cloud-computing solutions. Read more

Platforms: MacWinLinux
Deployments: CloudOn premise
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Callhippo

CallHippo is a cloud-based call center solution that helps mid to large size businesses with workflow automation and virtual telephony. The platform enables users to give detailed analysis to customers through call recordings. CallHippo... Read more

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Deployments: Cloud
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Voxbone

Take your business global in an instant with Voxbone’s enterprise-grade VoIP and messaging solutions, ideal for cloud-native organisations or those that are currently migrating to the cloud. Our global network spans 93% of the global... Read more

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Virtual Office by 8x8

Virtual Office is a collection of comprehensive web-based business VoIP solutions from offered by 8x8. Enterprise grade phone service, virtual meetings, mobile applications, virtual contact centers and more are available to help companies... Read more

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Recent recommendations: 53 recommendations

Platforms: MacWinLinux
Deployments: Cloud
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BlueJeans

BlueJeans is a cloud-based video conferencing solution that helps mid to large size businesses with text chat, content sharing, multiple participants and meeting recording. Blue Jeans delivers services through products including Blue... Read more

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Deployments: Cloud
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Vonage Business Solutions

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-enabled... Read more

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Deployments: Cloud
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Bright Pattern Contact Center

ServicePattern's SIP-based solutions focus on unifying customer engagement across telephony (both inbound and outbound), email, online chat and social media platforms adding the security and efficiency of the cloud. Read more

Platforms: MacWinLinux
Deployments: CloudOn premise
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SIP.US

SIP.US is a cloud-based business VoIP solution that provides SIP trunking services for IP-PBX systems and analog and digital telephone adapters. Key features include a Tier-1 redundant network, toll fraud protection, direct inward... Read more

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Deployments: Cloud
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NewVoiceMedia Cloud Contact Center

NewVoiceMedia’s tight integration with Salesforce is reflected in its AppExchange 5-star rating and the large number of positive reviews. The solution is designed to work in tandem with Salesforce capabilities and data to deliver... Read more

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Deployments: Cloud
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Business VoiceEdge

Comcast offers a cloud-based phone system known as Business VoiceEdge. Business VoiceEdge bundles SIP trunking service with hosted PBX applications. The PBX applications enable directory-based routing of inbound calls and communication... Read more

Platforms: MacWinLinux
Deployments: CloudOn premise
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Evolved Office IP Phone System

Evolve IP is a cloud-based IP phone and collaboration solution suitable for businesses with over 50 employees. It caters to multiple industries including credit unions, financial services, health care, legal, restaurants and veterinary.... Read more

Platforms: MacWinLinux
Deployments: Cloud
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Buyers guide


Last Updated: May 30, 2020

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.