5 Steps To Build A VoIP SIP Client: Full Guide for Developer

Mohamedasar Published On March 24th, 2025 Share it on

Not happy with the business phone system you currently have? 

It’s true that traditional office phones have their own disadvantages. You need expensive hardware, complicated wiring, and the maintenance is a bit costly as well. 

What if I say, your team will just need an app with VoIP solution on their computers and smartphones to make professional calls?

That’s what a SIP Client will do.

💡Did You Know?

Over 70% of businesses had switched to an internet-based phone system by 2023 for 2 reasons: To save money & to add new features. 

The bigger bonus, of course, is that these systems work anywhere there’s an internet connection. Teams can operate typically from anywhere:  while commuting, across any location, or when on a business trip.

In this guide, I’ll take you through what a SIP client (softphone) is and go over how to create one to meet your particular needs. 

Note: This article about building a calling app does not require you to have a technical background.

What is a SIP Client?

A SIP client is simply for phone calls through the internet. 

📌 A SIP client (or modernly called the softphone) is an app that runs on your computer, tablet or smartphone to work as a business phone.

Instead of using traditional phone lines to transmit voice, it makes use of the Internet. It sends your voice in the same way you would use Zoom or FaceTime, but majorly for business communication only.

The functionality is more like the traditional phones on your office desk. It has a dial pad, transfer, hold, and so forth. Just that, it is a software and not a hardware form.

This guide will cover a few technologies. 

I’ll briefly take you through the key terms you’ll read in this guide on and on. 

• VoIP: Voice over Internet Protocol. It is the technology that enables voice calls over the internet. It replaced the traditional phone lines with VoIP phone services, by converting voice data (analog) into digital signals that can be transmitted through the internet.
• SIP (Session Initiation Protocol): I’d like to call this protocol the language used for communicating phone calls across internet-based phone systems. It is a key protocol used in VoIP telecommunications networks and video conferencing systems. It is basically used to initiate, manage and terminate the communication sessions.
• Softphone: An instant messaging & calling app you can install on your computer or mobile device to use it as a telephone.
• SIP Client: Another name for a softphone. It is the software that connects to SIP-based telephone services.

You’ll come across these terms throughout this article. A basic coverage of these terms will help you understand the upcoming sections better.

Why Should You Build A VoIP SIP Client

When you compare with conventional phones, Internet-based telephone systems (SIP VoIP) offer several advantages to businesses. These are some of the benefits you will reap:

• Reduce expenses: There is a huge chance that you’ll lower your phone bills by 40-60%. Approximately, a company with 25 staff can usually save $500-$1,000 each month by transitioning when using a SIP client (internet-based phone communication system).
• Work From Anywhere: Your team can make calls from the office, home, or while traveling. They can use the same phone number and system.
• No Additional Hardware Required: All you need is a computer or a smartphone that you already use. You need not purchase any kind of desk phone, especially the expensive ones.
• Additional Features: Your team can enjoy modern features such as automatic call forwarding, voicemail-to-email, call recording, and team video meetings. You’ll not need any additional equipment or software to enable these features.
• Expands Alongside Your Business: Want to upscale? No worries. You can add additional users in just minutes. You’ll not need any extra hardware for this.

These are just some of the most important reasons I’d like to mention why building a SIP VoIP client is an important decision for your business.

To understand this further, let’s see how traditional and internet phones work, along with the difference in them.

Traditional vs. Internet Phones (SIP Clients)

Firstly, we’ll understand what happens when you make calls from a regular telephone and with a softphone:

Traditional Phone System

When you make a call on a traditional phone:

1. Your voice travels as electrical signals through copper wires.
2. These signals pass through your company equipment, probably a phone.
3. The signals reach the other person’s phone, through a dedicated phone line and specialized equipment.

Internet-Based Phone System (SIP VoIP)

You can expect this process at the backend, when you make a call with a softphone:

1. With VoIP in mobile devices, your voice is captured by your smartphone microphone
2. It is then converted into digital data
3. This data travels over your regular internet connection and reaches the recipient device
4. The recipient’s device converts this data back into sound

You can notice that you’ll not require a special phone for this. Just your existing internet service is sufficient. 

💡Did You Know?

An average business desk phone costs $800-$1000 per employee when you include hardware, installation, and maintenance. But with softphones, these costs nearly become ZERO because you’re using devices you already own.

Isn’t this a 2x benefit? Your expenses reduce + you get a modern communication system in place. If you are convinced with this fact, let’s move on to building your own business phone system.

How to Create Your Own VoIP SIP Client

Honestly, there’s no one way. You can build your Internet-based communication system in 3 different ways. Let’s explore them one by one.

Option 1: Use Ready-Made Softphone Apps (Easiest)

This is by far the simplest approach to implement softphones in your business. You just have to sign up with a SIP VoIP provider and use their recommended softphone apps:

What you’ll need:

• A SIP VoIP service provider account (similar to choosing a cell phone carrier)
• Their recommended phone calling apps installed on your devices
• Internet connection for each device

How it works:

1. You’ll sign up with a SIP provider to enableVoIP calling  capabilities
2. Next, you’ll download their softphone app to your computers/phones
3. The provider will give you login credentials
4. You’ll login with those details
5. From there, you’ll start making and receiving calls

Perfect for: Small businesses that need a simple, quick solution with only a minimal setup.

Option 2: Choose Your Own Softphone Apps (More Flexible)

For more flexibility, you can mix and match providers and VoIP calling apps:

What you’ll need:

• A SIP VoIP service provider account
• Your choice of VoIP calling apps (many free and paid options exist)
• Your provider’s connection settings

How it works:

1. Sign up with a SIP VoIP provider
2. Get your SIP account credentials and server information
3. Download your preferred VoIP apps to your devices
4. Configure the apps with your account information
5. Start using your customized system

Perfect for: Businesses that want specific features or interfaces that the provider’s default VoIP calling app doesn’t offer.

Option 3: Custom Development (Most Customizable)

For a completely customized solution, you can develop a custom SIP client:

What you’ll need:

• Software development resources (in-house team or outside help)
• A clear list of the features you need
• Development tools and SIP building blocks (SDKs)
• Time for development and testing

How it works:

1. Define exactly what you want your phone system to do
2. Work with developers to design the solution
3. Use development tools to build your custom system
4. Implement for your team

Perfect for: Any size of business with specific needs, or organizations with custom security requirements.

Building a Custom SIP Client: Step-by-Step Explanation

SIP client development is easiest when you know exactly what to build. Let’s simplify it by breaking down what you’ll need at each development step. 

Step 1: Make a Wishlist of Features

List out everything that you want in your phone system:

Basic features:

In the first stage, we’d recommend you to go with only the primary features such as calling capabilities, call hold, transfer, and conferencing. As you test and resolve bugs at this stage, it becomes easier to go with adding on team features like contact sharing, call forwarding and presence indicators. 

Advanced features:

As you gain more users to your SIP app, you can expand the feature list with call recording, voicemail transcription, and automated menus.  It is also a wide option to add integrations that can connect your calling app with customer databases or CRMs, email apps and helpdesk plugins. 

📌 MirrorFly Pro Tip Define the specific details of your requirements. Write them down with elaborate details. For example: Call record feature that can store call data for 90 days.This helps you create a roadmap clearly instead of having to change everything after you’ve built them all.

Step 2: Choose An SDK

If you are all set to carefully curate and build your VoIP application for your business, you’ll need SDKs (Software Development Kits). These are software which have pre-built libraries and tools you can use to create a SIP app 10x faster than writing every line of code yourself.

Got questions about customization when building with SDK?

No worries, SDKs like MirrorFly often come with a 100% customizable solution to build apps just the way you want in 48 hrs. You’ll have 1000+ features, full data control and above this, you can white-label your platform.

Step 3: Choose How You Want To Develop Your SIP Client

Human resources can be one of the key factors that impact your SIP client development. A few companies will have their own team and a few may look to outsource developers.

Considering all, here are 3 options we’d like to list:

• In-house development: You can use your own IT team, provided they have all the key skills related to build a SIP app platform. 
• Hire developers: There are dedicated SIP experts out there. You may hire an individual or a team of SIP specialists depending on your requirements, for this specific project.
• Partner with a solutions provider: The third one is an unique option where you can partner with a platform that specializes in communication solutions. This way you get your SIP system built and the maintenance taken care of.

If you are somewhere between a small and medium sized business, working with a reliable SIP solution provider can offer the best balance of affordability and customization.

Step 4: Design the User Experience

First impressions are the best impressions, they say. How your SIP app will look and feel at the first instance, makes it all about customer conversion. 

• What must your SIP client look like? What features should it have front and center? 
• If people have to transfer calls or set up conferences, which button will they use, what color they must be?
• Will people have the same experience in all the web & mobile VoIP apps the SIP client  is installed on?

Ask many questions like these and get on to build the best SIP platform out there. You can also avail a UI Kit to develop a complete app with pre-built features from trustworthy SIP VoIP solution providers.

Remember, building the best design is not about making the looks great alone. It is about making common tasks simple and quick, without clutter that may distract user experience.

Step 5: Development of SIP Client

I’d like to break this section into 2 parts:

• Developing a SIP Client Without an SDK
• Developing a SIP Client Using MirrorFly SDK

You can choose any of these 2 options to build your SIP Client. 

📌 MirrorFly Pro Tip Skip to Part 2, if you’d like to build your SIP Client in 48 hrs

Why We Recommend Building SIP Client With MirrorFly

We’ve discussed it all: options to use simple software phones from providers to fully customized VoIP solution.

For many companies, the best compromise lies somewhere in between: budget and features. MirrorFly offers them both.

And you witnessed it yourself. MirrorFly’s provides low-code and they are light-weight, easy to build and customize, when compared to building from scratch as we did in part 1.

You can customize the solution as much as you need, get 100% data ownership and full source code access. You can drive unlimited inbound and outbound calls, and deploy your platform on any servers. Additionally, you’ll be able to build the entire solution and launch it within 48 hrs. Who wouldn’t want a solution that’s quick, customizable and offers full control.

If you are excited about this solution, wait not a minute. Fill out this form and one of our experts will get in touch with you in the next 48 hrs!

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3. SIP Phones: What They Are & How They Work