📞 Asterisk: the open-source engine inside many PBX systems
An open-source telephony framework first released in 1999, now maintained by Sangoma Technologies. Not a ready-to-use phone system: Asterisk is the engine that telephony engineers and product vendors build on top of. FreePBX, Switchvox, and numerous commercial PBX products all use Asterisk under the hood.
⏱ 9 min read · 🌍 Open-source telephony framework · 📅 Updated April 2026 · 🔗 asterisk.org
🏢 What Asterisk is
Asterisk is not a product a business buys. It is a software framework for building telephony applications, first released by Mark Spencer and his company Digium in 1999, and now maintained by Sangoma Technologies, which acquired Digium in 2018. The framework runs on Linux and provides the underlying logic for call routing, voicemail, conferencing, IVR menus, queues, and SIP signalling. It is distributed under the GPLv2 licence (free to use, modify, and redistribute) with a separate commercial licence available from Sangoma for vendors who need to ship proprietary products built on Asterisk.
What makes Asterisk important for this comparison is not that a Luxembourg business would adopt it directly, but that many PBX products already use it. FreePBX is a graphical front end on top of Asterisk. Sangoma's own Switchvox is an Asterisk-based commercial PBX. A number of small and mid-size commercial PBX products in Europe and worldwide are built on the framework. Full disclosure: this site is maintained by a team connected to Mixvoip and Voxbi. This page covers Asterisk as an option because it is a legitimate path for organisations with telephony engineering capacity, and because understanding the engine helps evaluate the products built on top of it.
📦 What Asterisk offers
Asterisk is a toolkit, not a turnkey system. The components a builder uses:
🛠️ Telephony framework with a custom dialplan
The core of Asterisk is the dialplan: a configuration language that defines how calls route, when IVR menus play, which extensions ring, and how calls escalate or fall back. Dialplan logic can be written directly in Asterisk's extensions.conf file or in the newer AEL syntax, and more advanced deployments drive the dialplan from external applications via AGI (Asterisk Gateway Interface) or AMI (Asterisk Manager Interface). This is powerful and flexible, and it is also why raw Asterisk is not a ready-to-use system.
📞 SIP, PJSIP, and legacy protocol support
Asterisk speaks modern SIP through the PJSIP stack, plus older protocols including IAX2 (the Inter-Asterisk eXchange protocol, used between Asterisk servers), H.323, and traditional ISDN/PSTN interfaces through Digium and third-party telephony cards. This protocol breadth is part of why Asterisk is still used in environments that bridge legacy systems to modern VoIP.
🧩 Commercial and community distributions
The most common way to use Asterisk is through a distribution that adds a management interface and a curated set of configurations. FreePBX is the dominant community distribution (now also maintained by Sangoma). Switchvox is Sangoma's commercial distribution with support contracts. Other commercial PBX products use Asterisk internally without branding it as such. Telephony engineers can also run raw Asterisk with custom dialplans, which is the path for call-centre platforms and specialised telephony applications.
🔌 Bring everything else yourself
A working Asterisk phone system requires more than the software. The builder provides a Linux server, a SIP trunk from a local operator for external calls, SIP phones or softphones, backup infrastructure, monitoring, security hardening, and ongoing patching. In Luxembourg, the SIP trunk is typically supplied by an ILR-registered operator such as Mixvoip, Post Telecom, or Cegecom.
⚖️ Quick compare with two PBX rivals
Asterisk is an open-source telephony framework. This page compares it against the two options most often evaluated alongside it: the graphical distribution built on the same engine, and a managed service that removes the build entirely.
🧰 Asterisk
Open-source framework · this page
You are here
Deployment: self-hosted on Linux
Licensing: free (GPLv2), commercial licence optional
Sold via: not sold, adopted by engineers
SIP trunk: bring your own
Teams integration: custom build
Typical size: engineer-led deployments
🧩 FreePBX
Asterisk with a GUI
Deployment: self-hosted or hosted by partner
Licensing: free (GPLv3), paid commercial modules
Sold via: community and certified partners
SIP trunk: bring your own
Teams integration: via commercial module
Typical size: 10 to 500 users
Comparison reflects public information. Sources linked from each provider page. Not a ranking.
👥 Typical adopter profiles
Asterisk is adopted by engineers and vendors, not purchased by SMEs. Four common profiles:
👨💻 The telephony engineer building a custom platform
An in-house engineer or a specialist consultant building a phone system with requirements that commercial products cannot meet: unusual call flows, bespoke CRM integrations, custom billing, or protocol bridges. Asterisk is the natural starting point because its dialplan and API surface area expose every stage of a call to custom logic.
🏢 The PBX vendor or integrator as internal engine
A commercial PBX product or a custom integrator offering uses Asterisk internally without necessarily exposing it to the end customer. Switchvox (Sangoma's own), several European mid-market PBX products, and countless bespoke integrator builds all sit in this category. For the end customer, the experience is a product; for the vendor, Asterisk is the engine.
📞 The call-centre or contact-centre operation
A call-centre platform with specific requirements: predictive dialling, campaign management, real-time supervisor tools, detailed call data records, and integration with custom CRM logic. Several open-source and commercial call-centre platforms (Vicidial, Issabel, and others) are built on Asterisk because the framework handles the telephony layer cleanly and leaves the workflow layer to the application.
🔬 The research or education deployment
Universities, telecom labs, and research projects use Asterisk to prototype protocol work, teach VoIP concepts, or run experimental deployments. The cost of a proof of concept is essentially zero, which suits environments where budget is scarce and engineering time is abundant.
🎯 Where Asterisk stands apart
Three positioning points worth weighing before adopting Asterisk rather than a product built on it.
🎛️ Unlimited customisation at the telephony layer
Nothing in the commercial PBX market matches the depth of control Asterisk gives to a competent engineer. Call flows that would require a vendor feature request in a commercial product are a few lines of dialplan in Asterisk. For genuinely novel telephony applications this is decisive.
💸 Zero licence cost, non-zero total cost of ownership
Asterisk is free to use. A running Asterisk phone system is not. The total cost includes the Linux server or VM, telephony engineering time (design, configuration, testing, ongoing changes), SIP trunk subscription, security patching, backups, monitoring, and incident response. For a small Luxembourg SME, the engineering hours usually outweigh the savings on licensing compared to a managed service. For a call-centre operation or a PBX vendor, the economics reverse.
🛠️ No product, no support contract, no procurement path
Because Asterisk is a framework rather than a product, there is no vendor to contract with, no support SLA, and no procurement process in the conventional sense. Commercial support is available through Sangoma and through Asterisk consultancies, but this is a separate engagement for expertise, not a product licence with support attached. Organisations that want a vendor relationship with defined service levels typically pick a product built on Asterisk rather than raw Asterisk itself.
📚 Terms you can look up
Not sure what something on this page means? The pbx.lu glossary explains each in plain language.
🧩 Decision tree
Two honest recommendations based on what the organisation actually needs.
✅ Build on Asterisk if
- You have, or can hire, a telephony engineer who already knows dialplan, SIP, and Linux administration
- Your requirements go beyond what commercial PBX products offer (custom call flows, protocol bridges, bespoke billing, specialised call centre logic)
- You are a PBX vendor, integrator, or call-centre operator where the engineering investment pays back across many deployments or seats
- Licence cost avoidance matters more than time-to-deployment and support SLAs
🟡 Use a product built on Asterisk (or a managed service) if
- You need a working phone system in weeks, not months
- Day-to-day moves, adds, and changes should be a GUI task, not a dialplan edit
- You want a vendor relationship with support, patches, and a defined SLA
- Your business is a standard SME and the telephony is a means to an end
🔎 Other providers worth considering
If raw Asterisk is not the right path, these are the logical next pages to check.
Same category · other PBX products and UC platforms
Different category · Luxembourg operators and SIP trunks
📦 Post Telecom
Incumbent national operator, SIP trunks and hosted telephony
🔵 DEEP Telecom
POST Luxembourg's B2B brand, SIP trunks and enterprise telephony
❓ Common questions
Is Asterisk a phone system or a framework?
A framework. Asterisk provides the engine, the telephony protocols, and the dialplan logic, but not the administration interface, user management, or workflow features that most people expect from a PBX. A working Asterisk phone system is always the result of a build effort, either by an in-house engineer or by adopting a distribution like FreePBX that wraps Asterisk with a GUI.
Can a small business in Luxembourg use Asterisk directly?
Technically yes. Practically it is rarely the right choice. Raw Asterisk requires a Linux server, telephony engineering time, SIP trunk configuration, and ongoing maintenance. For most Luxembourg SMEs, either a product built on Asterisk (like FreePBX with a partner) or a managed service is a better fit. The engineering cost of running raw Asterisk tends to exceed the licence savings for small team sizes.
Who maintains Asterisk today?
Sangoma Technologies, a Canadian company that acquired Digium (the original Asterisk creator) in 2018. Sangoma also maintains FreePBX and sells Switchvox, a commercial PBX built on Asterisk. The core Asterisk project remains open source under GPLv2 with an active developer community.
What is the difference between Asterisk and FreePBX?
Asterisk is the telephony engine. FreePBX is a web-based administration interface built on top of Asterisk. FreePBX lets administrators configure extensions, ring groups, IVR menus, queues, and voicemail through a browser instead of editing Asterisk configuration files directly. Both are open source, both require self-hosting, and both rely on the same underlying Asterisk framework. FreePBX is the accessible starting point for most open-source PBX deployments.
Is Asterisk really free?
The software is free under GPLv2. The running system is not. A working Asterisk deployment involves server infrastructure, SIP trunk costs from a local operator, engineering time for configuration and ongoing changes, and maintenance for security and updates. Sangoma also offers a commercial licence for vendors who ship proprietary products based on Asterisk, and paid commercial support contracts for organisations that need defined SLAs.
What is a dialplan?
The dialplan is the set of configuration instructions that tells Asterisk how to handle calls: which extensions ring, when to play an IVR menu, how to route based on caller ID or time of day, when to fall back to voicemail, and how to integrate with external applications. It is written in Asterisk's own configuration syntax (extensions.conf) or in higher-level abstractions and is the point where telephony engineering meets business logic.
When should a business pick a managed service instead?
Pick a managed Cloud PBX when the phone system is infrastructure rather than a product. If the business wants calls to work, reporting to be available, and support to exist when something breaks (without running a server or hiring a telephony engineer), a managed service aligns the cost model with the actual requirement. Asterisk and its distributions shine when telephony is part of the core product or operation, not a supporting function.
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