SIP API: Everything You Need to Know

Posted on April 26, 2023

If you are a developer for a business, you have or will likely be responsible for integrating its business communications into a software solution or system. Your client or company may be considering SIP, a technology that has proven to be an apt solution for many organizations and their growing need for cost-effective, reliable communication for on-site and remote users. According to Globe Newswire, the global SIP market is expected to grow to nearly $24 billion by 2026, with a market value of just over $13 billion in 2021.

This post will introduce you to SIP if you are unfamiliar with the technology and guide you through the benefits of SIP for business. We will explore ways to implement a SIP API and how you and your company or client can benefit from choosing a reputable SIP API provider for your integration that will provide reliable communication for critical applications.

What Is SIP?

As a developer, you may already know that Session Initiation Protocol (SIP) allows your business or client to communicate by sharing voice, video, files, fax, and instant messages over a network. SIP allows users to communicate directly over the internet or through a carrier’s public switched telephone network (PSTN). 

How Does SIP Benefit an Organization?

As organizations become more decentralized, allowing employees to work from remote locations, a solution that provides security, connectivity, and reliability is needed to maintain communications. SIP trunking offers an ideal solution for organizations that use multiple communication channels in an on-site, hybrid, or remote office setting. The business can manage communications from a central location without costly on-site infrastructure.

SIP allows you to integrate Voice over Internet Protocol (VoIP), so your business can continue to use its VoIP provider. You can use SIP trunking to provide your client or company with numerous simultaneous communication channels. Unlike trunking provided by private rate interface (PRI), SIP trunks are not limited to 23 channels per T-1 connection and offer near-limitless simultaneous calling capabilities, as long as the business has the necessary bandwidth.

Related: Questions to Consider as You Look to Scale Your Programmable Voice Solution

Employees can use company-owned SIP trunks from IP phones, software phones, and mobile phones. SIP also works with IP private branch exchanges (IP-PBX) and virtual PBX, allowing for various configurations. No matter where a user calls from, they will have high-quality, secure, and low-cost voice service—and they can mask their phone number with the business phone number.

Building vs. Buying an API

As a developer, your business or a client may ask you to integrate SIP into their app, software, or customer relationship management (CRM) solution. You can probably build an API for your client or business, but buying an API can provide several benefits. 

An API, even for the simplest program, can take days to build from scratch. It can take months to provide a polished and functional communications API. Buying an API is preferable when your company or client needs an enterprise-grade SIP trunk to integrate into their software or systems quickly.

A SIP API from a reputable communications platform will have your business or client’s communications up and running in minutes, with only a few lines of code to add to the existing software. The organization will offer a fully functional SIP trunk with seamless integration, satisfying your company or client and making your job easier.

What Are the Advantages of SIP API for Developers?

If you have decided to buy a SIP API, you will have a ready solution for your client that offers the following benefits.

Easy Integration

As mentioned, a SIP API can be integrated with a few lines of code and up and running in minutes. APIs for communication typically use representational state transfer (REST) architecture. REST APIs are known for being resource friendly and highly compatible. They work well with common programming languages, use popular data formats like JSON and CML, and use well-established HTTP commands like PUT and GET.

REST allows you to work with the programming language your business uses or you are most comfortable with. A SIP API written in REST reduces the bandwidth and processing power required, allowing it to run with minimal resources. This is an added benefit for SIP trunk users because much of the processing is done on the client side rather than the server side.

Security and Maintenance

In addition to being easy to integrate, a SIP API from a reputable platform will be maintained by the provider using a version control system like GitHub. This allows you to ensure your company or client uses the most up-to-date API—one that has been tested before release. When you develop an API on your own, maintenance and testing has to be done by you or your company, which can lead to delays and issues.

APIs are inherently exposed to the public and are a primary vector for exploits and attacks. Gartner predicts that by 2025, over half of data breaches will be due to unsecured APIs. Your client or company’s communications APIs can transmit sensitive business and client information, so ensuring the surface is secure from vulnerabilities is critical.

When you rely on a reputable API provider, your API is maintained and secured in world-class data centers with professionals working 24/7 to ensure the data is safe. For many small and medium-sized businesses, this level of security is cost prohibitive without an API partner.


A reputable cloud-based communications platform can provide exceptional reliability, uptime exceeding 99.999%, and rate centers worldwide to ensure your client or company’s users can always access their SIP trunk. While achieving excellent reliability using a traditional PSTN is possible, the cost would be significantly higher, especially if the client or company requires international calling capabilities.

A SIP solution provided by a reputable platform avoids aggregators that can increase calling costs internationally and reduce network reliability. To avoid interruptions, they can proactively identify network outages and route callers to a known-working failover network.


When you trust a reliable platform with a global footprint, your client or company’s SIP communications can scale indefinitely. With the scalability and elasticity of the cloud, the only limitation is a business’s bandwidth. The organization and its users will have network capabilities to match the demand during increased usage.

Related: Programmable SIP: What You Need to Know When Getting Started

The elasticity of the cloud allows the network to scale back down when usage decreases, and your client or company will not be left without the capacity it needs or costly infrastructure that they rarely utilize. Scalability is especially helpful for SIP trunking, as new channels can be added to the trunk as necessary.


With the right partner, your company or client will not face any penalties for using the near-limitless potential of their cloud-based SIP trunk. A metered or per-minute plan offers the most flexibility to fully benefit from the scalability of the cloud. 

Your company or client will only pay for network usage during a specific billing period, so they won’t need to pay for unutilized calling capacity. With a metered plan, you can evaluate and test the API without a significant upfront investment, and since the SIP trunk is on the cloud, minimal equipment is required.

In addition to metered plans, there are also flat-rate payment plans, where the company buys a set amount of minutes for SIP calls. If the company exceeds its usage limits, it can be penalized, and if it does not make the number of calls it expects, it will still be stuck paying for the excess service. 

We recommend looking for a partner that offers the capabilities your business or client expects with a flexible, metered plan.

Find the Right SIP API Partner

An excellent API provider will make implementations as smooth as possible, with a flexible and light REST API and documents to help you get started in your preferred programing language. The best providers offer quickstarts in Docker to help you implement microservices like e911 with ease, as well as offering use case articles to help you explore the potential of the API. 

Your SIP provider should also have a robust network with rate centers worldwide and physical failovers to ensure users always have reliable calling. The right partner will allow your company or client to scale up and down using its cloud-based network, with transparent and flexible pricing. Additionally, reputable SIP providers will allow you to bring your own carrier and devices, like IP phones and PBX. 

Flowroute offers industry leading API solutions, including SIP trunking and SMS/MMS, as well as reliable, worldwide calling. We protect your SIP trunk with authentication, destination restriction, and toll fraud prevention. You and your client or business can take advantage of a scalable and flexible SIP API solution on a metered pricing plan. Get started with a free Flowroute account today.