Open-source Mitel alternatives

Asterisk is an open-source PBX and telephony toolkit. It acts as middleware between internet and telephony channels on one side and telephony applications on the other. The project describes itself as supporting far more than internet telephony, with extensive support for traditional public telephone network connections as well. The codebase is written in C.

Most deployments today use VoIP and SIP exclusively, but Asterisk can also interface with TDM and analog services when the right hardware is installed. Supported telephony hardware includes Sangoma analog and digital interface cards, full-duplex sound cards supported by PortAudio, and the Xorcom Astribank channel bank. It is developed and tested primarily on GNU/Linux and reportedly also runs on macOS and the BSD variants.

Asterisk is built from source and needs a compatible compiler and development libraries, so it suits telephony engineers, service providers and administrators comfortable with that process. The project strongly urges new operators to read its security documentation before configuring a server, and its change logs are the starting point when upgrading between versions.

FusionPBX is an open-source web interface and management layer for FreeSWITCH, the telephony platform that handles call routing. It turns a FreeSWITCH installation into a domain-based, multi-tenant PBX and voice switch, so one server can serve several separate organizations, each with its own extensions and settings.

Beyond ordinary office phone features, the project says it can act as a call center server, fax server, voicemail server, conference server and voice application server. Configurable features include unlimited extensions, voicemail-to-email, device provisioning, music on hold, call parking, automatic call distribution, interactive voice response, ring groups, find me and follow me rules, and hot desking. A flexible dialplan system allows custom call logic.

FusionPBX is written in PHP and installs on Debian, Ubuntu LTS, FreeBSD and CentOS using a scripted installer. The installer sets up FusionPBX, FreeSWITCH and its dependencies, along with Nginx, PHP-FPM, PostgreSQL, Fail2ban and IPTables. High availability and redundancy are listed among its capabilities.

Linphone Desktop is an open-source softphone for voice and video calling and instant messaging over IP. It is based entirely on the SIP protocol and handles calling, presence and messaging features. The project is developed by Belledonne Communications, and this GitHub repository mirrors the official git repository.

Topics on the repository include conferencing, chat and messaging. The app is built with Qt 6, requires a C++17 compiler, and depends on the Linphone SDK, so building from source means installing the SDK dependencies and setting up the Qt environment. Supported features and RFCs are listed in the project documentation and wiki.

Linphone is dual licensed. It is free under GPL-3.0 for open-source use, and Belledonne Communications also sells a proprietary license for a fee to companies that want to use it in closed-source applications.