GW-SIP: I just wanted to make calls from my PC. Now I have my own app.

Starting a company comes with plenty to do: website, quotes, admin – and in between, you should also be reachable by phone for customers.

For Geissmann Webconsulting, I wanted to use my landline number directly on my computer. No extra phone on the Salt Fiber Box, no additional device on the desk. Just a headset and a free desktop app.

That was the plan, at least.

A few detours later, I had built GW-SIP 1.0: my very own SIP softphone for Windows. It wasn't originally on the founding checklist. But projects like this rarely announce themselves in advance.

GW-SIP is now ready for the beta phase. Publication on my website is planned: free of charge, with no third-party ads, and with publicly accessible source code.

Finding a free SIP app – how hard can it be?

A softphone turns your computer into a telephone. With a suitable SIP account, you can make calls through an app instead of a separate phone. All you need are the credentials, a suitable network connection, and a microphone with speakers or a headset.

That's exactly what I was looking for at my workstation. My Salt line was the starting point: I wanted to use my landline number on the desktop without buying an extra phone.

There's certainly a choice out there. But my search quickly showed that “free” is sometimes more the start of a price negotiation than the end of one.

The app costs nothing? Lovely. The feature I want belongs to the paid version? Of course. Somebody has to pay for the software development, after all.

With the truly free solutions, I then understood quite well why people spend money on a softphone. Some things work, but they require a certain willingness to befriend them.

All perfectly legitimate. Good software doesn't build itself. But by then I'd had a thought that tends to lead technically minded people to long evenings: I could just build this myself.

Alright, I'll do it myself! The app, that is.

Since I'm currently training in application development, the project fit rather well. There was a real need. The motivation was there too. What could possibly get out of hand?

At first, I wanted a clear dial pad and the ability to set up a SIP account. Then a call list would be handy. A phone book, too, really. And since the app is running anyway, it might as well tuck itself into the Windows notification area when minimized.

That's how software grows: one “that would be handy too” after another.

The result is GW-SIP 1.0 by Geissmann Webconsulting, built with C# and WPF on .NET 8. And with considerably more features than I had on my list at the start.

I'm proud of that. What seemed like a small task has turned into an application that I'd like to make available to others soon.

Phoning with mouse, keyboard and Swiss numbers

GW-SIP can be set up with a SIP account. That includes registrar, domain, port, username and password. The dial pad can be operated with mouse and keyboard – including the number pad, Enter, Backspace and Esc.

The feature set includes calling, holding and hanging up, muting the microphone and speaker output, tone dialing (DTMF) for phone menus, and support for the G.711 voice codecs in the PCMU and PCMA variants.

Swiss number logic is covered too: “079…” becomes “+4179…”, “00…” becomes “+…”. Short numbers such as 112, 117, 118 and 144 stay unchanged. After all, the app is supposed to take work off your hands, not hand out a little formatting exercise with every phone number.

For emergency calls, it is the SIP provider that decides on the correct regional routing. Passing the number through unchanged does not guarantee this on its own.

A phone book that knows more than just the number

Besides name and number, the phone book has room for company and notes. A search helps you find entries again. On first launch, “Geissmann Webconsulting” is already entered. A little home advantage is allowed.

The call list distinguishes between incoming, outgoing and missed calls. There's also a journal per number. With a click, a number can be loaded into the display for a callback.

Optionally, number recognition via search.ch can be used. This requires your own API key.

Phone numbers from the browser are handled as well: links with tel:, sip: or callto: open a selection window. There you can dial the number or add it to the phone book. At least here, retyping numbers is a thing of the past.

Ringing without having to wear the headset

One detail was especially important to me: for ringing, notifications and the startup sound, you can choose a separate output device – independent of the headset. After all, a headset sitting on the desk is a surprisingly discreet place for a ringtone.

There are also indicators for registration, missed calls and new messages. In Do Not Disturb mode, incoming calls are signalled silently with a small notification.

When minimized, GW-SIP retreats to the Windows notification area. From the menu there, you can open the app, switch it to “Do Not Disturb” or quit it. If you like, you can also have GW-SIP start minimized with Windows.

And then a few more features came along

The scope also includes a local answering machine with its own greeting and recording, an adjustable ring duration for the answering machine, call forwarding options for always, when busy and when unanswered, and optional call recording with a note on Swiss law.

By this point at the latest, it was clear: “I just need a quick phone app” had turned into a proper development project.

What does GW-SIP need on Windows?

GW-SIP is designed for Windows 10 version 1809 or later and Windows 11, both 64-bit. You need the .NET 8 Desktop Runtime in the x64 version, a microphone with speakers or a headset, a suitable SIP account with the corresponding credentials, and a network connection to the SIP server.

Installation is per user and needs no administrator rights. The interface is in German.

Video calls and contact import from vCard, CSV or Google are not part of the current feature set. At some point, a first version has to be allowed to be just a first version.

What's next: free beta and public source code

GW-SIP is now ready for the beta phase. Next, I'd like to publish the app on my website and make it available for interested people to try out. Free of charge and without third-party ads. A little bit of Geissmann Webconsulting is allowed in there. If you're building your own app, you're entitled to put your name on it, after all.

I will also publish the source code in a public Git repository. If you find a bug or have an improvement in mind, you can contribute directly to the code. So a “Couldn't we …” is very welcome to become a concrete contribution.

The beta is meant to give me the chance to gather experience with different SIP configurations and in everyday use. Feedback helps to find bugs and to keep improving usability.

A stable version is to follow. More features are already planned, and suggestions are explicitly welcome. I've learned in the meantime that “just one more small feature” is a very elastic term. Still, I'm happy to hear your ideas.

SIP telephony tailored to your own business

GW-SIP can also serve as the basis for custom solutions. For business customers, adaptations to branding and feature set as well as special developments around SIP telephony are possible.

Whether it's your own look and feel, additional features or a specific workflow in your daily work: if the standard solution doesn't quite fit, we can talk about it – and develop the right solution if needed.

Such custom adaptations are not part of the free scope of the open-source project. They are carried out as a regular, paid development engagement according to an agreed scope. The publicly available standard version of GW-SIP remains free of charge regardless.

So the app is free. The tailor-made company solution does need a quote, though – the coffee for the development has to come from somewhere, after all.

From my own need to my own software project

I wanted a landline app for my workstation. What I got on top of that was a rather practical bit of further training.

With GW-SIP, the user interface, telephony, audio, contacts and local data storage all had to come together. You quickly notice how many decisions can hide behind a button that simply says “Call”.

That's exactly the connection I like: recognizing a need of my own, developing a solution, and learning along the way.

Was that the shortest path to a phone app? Probably not. Am I glad it turned into GW-SIP? Absolutely.

Interested in the upcoming beta, have a feature idea or a specific customization request? Then I'd be happy to hear from you via the contact form of Geissmann Webconsulting.

Frequently asked questions about GW-SIP

What is GW-SIP?

GW-SIP is a German-language SIP softphone for Windows from Geissmann Webconsulting. The application includes telephony, a phone book, a call list, a local answering machine and call forwarding options, among other things.

Is GW-SIP free?

The planned public beta will be made available to interested people free of charge and without third-party ads. References to Geissmann Webconsulting may be included. Independently of this, the terms of the respective telephony provider apply to the SIP line and calls.

Where can I download GW-SIP?

The beta release is planned for the Geissmann Webconsulting website. Once it is available, information on downloading and setup will be provided there.

Will the source code be published?

Yes, the source code is to be made available in a public Git repository. That lets interested people follow the development and contribute their own improvement suggestions or code.

Can I use my existing landline number on my PC?

A suitable SIP account that the respective line or provider supports is required. Among other things, you need a server address, username and password. An existing landline number alone is not enough for setup.

Does GW-SIP work with Salt?

My Salt line was the starting point for the project. Whether GW-SIP can be used on a specific line depends on the available SIP access and the respective configuration. This does not amount to a general compatibility guarantee for all Salt lines.

Can GW-SIP be customized for my business?

Yes. Adaptations to corporate branding and feature set as well as special SIP developments are possible. These custom services are not part of the free open-source offering and are carried out as a regular, paid engagement by arrangement.

Are more features planned?

Yes. A stable version is to follow after the beta. More features are planned; ideas, feedback and contributions from real-world use are welcome.

Sandro Geissmann | Geissmann Webconsulting

All articles are general professional background information and do not replace individual legal or professional advice.