Senior VoIP Engineer

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Senior VoIP Engineer

Collaborate with our other SIP stack developers to solve problems, create new features, and introduce new technologies to the infrastructure of our VoIP telephony platform. 

Full-time / Part-time · Groningen

We are looking to strengthen our infrastructure team with an experienced SIP stack developer for our telephony platform VoIPGRID. You would work on our telephony stack, developing and maintaining our SIP stack as well as creating new features and introducing new technologies. You will be working with two other SIP stack developers, which allows for a lot of discussion and collaboration. 

For VoIPGRID we support telephony over traditional hard phones, a mobile app for iOS and Android and a progressive web app (WebRTC). We are active in four countries (The Netherlands, Belgium, Germany, and South-Africa), with servers in The Netherlands and South-Africa (meaning some fun latency issues between servers, databases and customers!). 

Our customers expect their telephony to work 24/7, so all our infrastructure is redundant. Our SIP stack consists of OpenSIPS and Asterisk, with a MySQL database and a Python/Django web app. We also have a custom Golang application that sits in between the web application and the telephony layer. Last but not least we are slowly moving microservices and other services to Kubernetes. 

As a developer, you have experience with some sort of SIP development, for example with OpenSIPS or Kamailio, as well as Asterisk development. You know your way around unit- and integration testing (we use SIPP and/or pjsua). Problems that occur don’t scare you, but rather trigger you to find the root cause, come up with solutions, and be part of the team to implement them. You constantly look for ways to improve our product and our work processes, and aren’t afraid to give your feedback to the team. Sharing knowledge comes naturally to you, as well as learning from others, especially if it is in the form of open source projects, such as our OpenSIPS exporter.  

Your professional profile


  • Have a great command of English, our working language

  • Have experience with C/C++ development

  • Have experience with SIP

Bonus points if you:

  • Have more specific Asterisk experience, such as Chan_sip/PJSIP and dial plans

  • Have experience with Go, Elixir, and/or Rust

  • Know your way around GDB debugging

Our stack:

  • Asterisk
  • OpenSIPS
  • Python
  • Golang
  • Mysql
  • Django
  • Kubernetes
  • Saltstack
  • Prometheus/Grafana
  • Homer
  • Proxmox/KVM

About Spindle

Devhouse Spindle is a growing and ever-changing organization on a mission to connect the world using open and free communication. With almost 60 colleagues, we develop the tools that make this possible such as VoIPGRID, our award winning telefony platform. Alongside our VoIP platform we develop an app (both Android and iOS versions), a webphone, and a browser plugin which allow you to use the platform wherever you are.

Next to the tools we develop, we also connect people through the foundation, and the open source community, the Open VoIP Alliance. Spindle is located in Groningen, a beautiful city known for its innovation and the second fastest growing tech city in the Netherlands.  

Working at Spindle

If you look around the office, you’ll notice we do things a bit different around here:

  • We organize ourselves using a system called Holacracy. We believe every colleague is able to contribute to the organization rather than relying on a traditional hierarchy. Having no managers comes with extra responsibility to take ownership of your work and set priorities that help to further the organization.

  • We work with a “build, measure, learn” mentality and open mindset. We recognize that not everything you do is going to work right away. We praise experimentation and reward trying something new, even if the lesson is to not try it again.
  • We have an open and transparent salary system. Every colleague is placed in the pathway and a level best fitting their education, experience, and visible behavior. We encourage growth and have clear guidelines and expectations for doing so.
  • We are a diverse and inclusive team of international coworkers. We value the differences that each person brings to the table and think that it's those differences that strengthen our organization.
  • We strongly believe in open source. We show this by open sourcing our code when possible, using other open source projects for our VoIP platform, contributing to projects, and we have even started the Open VoIP Alliance to encourage collaboration when it comes to VoIP open source software.

What we offer

  • A relaxed and welcoming culture with celebrations, events, and trips

  • A competitive salary and good pension benefits
  • An annual study budget and study days for personal and professional growth
  • Other benefits that contribute to your health, well-being, and work/life balance 

Join the team

You can apply for this job opening using the button below.

Want to know more about this job, the employee benefits, or Spindle? Don’t hesitate to contact Dick on 050-8009078 or

Please note that we are currently not hiring for remote work. You need to have an EU Working Permit (Orientation Year Visa not included) in order to be applicable for this position.