Integrating SIP Telephony into Element: Linphone Web Enables Outbound Calling

At the 2025 DINUM Hackathon, a successful integration of Linphone Web into the Element communication platform demonstrated the potential to enable outbound telephone calls directly from Element’s interface. This milestone paves the way for extending Element with real-time SIP telephony, offering new communication capabilities based on open and interoperable technologies.

Key Figures — DINUM Hackdays 2025

Organized by France’s Interministerial Directorate for Digital Affairs (DINUM), the Hackdays event brought together a global community of developers and digital experts focused on modernizing public digital services:

• 258 developers
• 17 countries represented
• 53 participating companies
• A mix of public sector agents, students, startups, open source contributors, and major tech firms

Linphone Web Integrated into Element: A Step Toward Unified Telephony

Element is an open-source communication client built on the Matrix protocol, providing secure messaging and internal calling. While it supports intra-platform calls, it lacks native capabilities for calling external phone numbers (mobile, landline, or third-party services).

Belledonne Communications is developing Linphone Web, a new project the teams have been actively working on for several months. It represents a major evolution of Linphone, designed to run directly in web browsers without requiring the installation of a heavy client.

During the hackathon, the integration of Linphone Web technically validated the addition of outbound telephony to Element. Thanks to this component compatible with the SIP (Session Initiation Protocol) standard, a direct interconnection from the web client was successfully established. Part of the work involved adapting the Linphone Web interface to integrate more naturally into Element’s interface, ensuring a consistent and seamless user experience. The integration is thus performed natively within Element’s interface, without relying on any third-party application, while meeting ergonomic and security requirements.

Objective: Enable Outbound Telephony via PSTN

The integration addresses a key challenge: providing users with the ability to place calls to external telephone networks. Using a lightweight, browser-compatible SIP client such as Linphone Web is a first step toward building a full SIP-to-PSTN gateway, allowing Element to connect seamlessly with the traditional Public Switched Telephone Network (PSTN).

Project Timeline

Preparation Phase

One week before the hackathon, initial internal work was carried out to lay the foundation for the project.
The objective: integrate Linphone Web into the Element application to enable external calls.

• A functional prototype was created, featuring a call button integrated into the interface.
• Technical audio tests confirmed that outbound calls were working properly.

The Three Days of the Hackathon

Day 1 – Project Kickoff

• Setup of the development environment and sprint planning.
• Development began with the addition of the call button and integration of the Linphone component into the chat interface.

Day 2 – First Real-World Tests

• An outgoing call to a mobile number was successfully made and confirmed to be fully functional during testing.

Day 3 – Finalization and Demonstration

• The interface was improved for a smoother user experience.
• The project was presented to a jury, including a live demonstration of an external call.

What Was Achieved During the Hackathon

The integration was carried out collaboratively by the Linphone team and technical experts from DINUM. Several key features were successfully implemented:

• Connection to a SIP trunk for routing outbound calls
• Audio call initiation directly from the Element interface
• Use of an Element widget to dial phone numbers from a chat room
• Addition of a global call button within Element’s UI
• Adaptation of WebRTC media streams to the RTP format used in SIP telephony

Impact on User Experience

Until now, users had to rely on separate tools for voice calls to external numbers. This integration enables users to initiate SIP calls directly from Element, streamlining workflows and enhancing the overall communication experience.

Toward an Open, Interoperable Telephony Stack

This experiment showcases the potential of open source VoIP solutions to enhance collaborative platforms like Element with robust, standards-based telephony features.

Learn More & Next Steps

This proof of concept serves as a concrete foundation for any organization looking to:

• Integrate SIP telephony into Element
• Deploy a gateway to PSTN for external calling capabilities

Belledonne Communications, the team behind Linphone and a recognized expert in real-time open source communications, is available to support organizations in designing and implementing flexible, secure, and standards-compliant VoIP infrastructures.