Asterisk

Open-source telephony engine for building flexible VoIP communication systems

Updated July 27, 2026

Asterisk Overview

Asterisk is a widely adopted open-source telephony framework used to build PBX systems, VoIP gateways, and unified communications solutions. It enables organizations and developers to design custom voice, video, and messaging applications using standard hardware. Known for flexibility and scalability, Asterisk supports SIP, IVR, call routing, conferencing, and integration with CRM and business tools across industries.

Key Features

  • Open-Source PBX Engine: Build and customize complete VoIP and PBX systems without vendor lock-in.
  • SIP & VoIP Support: Native support for SIP, IAX, WebRTC, and multiple codecs.
  • IVR & Call Routing: Design advanced interactive voice response flows and call logic.
  • Conferencing: Audio and video conferencing with flexible participant control.
  • Scalability: Suitable for small offices up to carrier-grade deployments.
  • Integration Ready: Connect with CRMs, databases, billing systems, and APIs.
  • Multi-Platform: Runs on Linux and supports standard server hardware.

Pricing

Plan

Price

Featured
Asterisk (open source) $0 Full framework under GPLv2; latest LTS release 22.10.1 downloads free from asterisk.org, as do the Certified Asterisk builds
Commercial license Quoted by Sangoma Needed only to ship modified Asterisk inside a proprietary product; Sangoma is the exclusive licensor and says fees vary with the application and the scale of its use
Add-on modules G.729 codec keys $8 per concurrent call; other modules quoted Fax For Asterisk, the Digium Phone Module, HPEC echo cancellation and the Siren, SILK and Opus codecs come from Sangoma
Support subscription Quoted by Sangoma Five levels covering Core modules; Level 5 adds a negotiated SLA with guaranteed response and resolution times and is aimed at OEMs

Apart from the G.729 key, none of the paid options carry a public price list: Sangoma quotes licensing and support case by case.

Pricing source: https://www.asterisk.org/products/software/licensing/

Pros

Competitor

Pros
Cisco Unified Communications Manager Cisco licensing plus hardware runs into serious money before the first call. Asterisk is $0 under GPLv2 and only costs money if you need a non-GPL license or a Sangoma support contract, and reviewers describe using it to retire an expensive phone system outright.
FreePBX FreePBX is built on Asterisk, so the two are not really rivals: FreePBX adds the GUI, Asterisk keeps the dialplan and AGI scripting that reviewers use to add features and wire in other software. Going straight to Asterisk suits teams that want call logic the GUI cannot express.
3CX 3CX charges per system by simultaneous calls and renews annually. Asterisk has no license meter at all, and the project counts installations in about 150 countries and roughly 11.5 million downloads a year, from single-office setups to nationwide multi-site networks.
Avaya Aura Avaya sells a finished platform; Asterisk sells nothing and lets you build the platform. SIP, IAX, WebRTC, IVR, queues and conferencing are all in the source, and Certified Asterisk builds with security releases exist for organizations that need a supported baseline.
Microsoft Teams Phone Teams Phone is a subscription tied to Microsoft 365 and its call control stops where the product stops. Asterisk runs on standard server hardware you already own, integrates with CRMs, databases and billing systems through AGI and APIs, and an 85,000-member community plus the Asterisk forum carries most of the support load.

Cons

Competitor

Cons
FreePBX FreePBX wraps Asterisk in a web GUI and, from version 17, installs on Debian with Asterisk and the tooling bundled in. Bare Asterisk means editing dialplans and config files by hand, so a shop without Linux and VoIP skills gets a working PBX faster with FreePBX.
Cisco CUCM Asterisk support comes from Sangoma as a separate subscription, and only Level 5 carries a negotiated SLA with guaranteed response times. Cisco sells the platform, the phones and the support contract as one accountable package, which matters when a voice outage has to have an owner.
3CX 3CX publishes system prices by simultaneous call count, from $295 a year at the smallest tier, with a guided setup and its own desktop and mobile clients. Asterisk costs nothing to download but the configuration work, upgrades and security patching are all yours.
Twilio Twilio hands over managed global infrastructure behind an API. With Asterisk you own the servers, the trunks, the scaling and every security release, which is real operational load for a team that wanted communications as a service.
Avaya Aura Avaya ships contact center and collaboration features plus a certified hardware list out of the box. Asterisk gives you the engine; conferencing, IVR and CRM links exist but are assembled, and matching interface cards to a provider’s service is a documented source of setup pain.

Reviews

  • CCapterra Review (Rating: 4.5/5): Asterisk allowed one system administrator to interconnect government branches nationwide via VoIP and scale operations without issues, while also integrating with specific business applications. Another long-term user who relied on it for 20 years called it the “best software at no cost,” praising its open standard, full customizability, and AGI Scripts that add features and connect easily with other software, though setup can become complicated when server cards and telephony provider services must match.
  • G2 Review (Rating: 4.6/5): Asterisk helped teams replace high-cost phone systems entirely and provided a complete telephony solution with texting support baked into many installs. Strong community support and the VOIP feature earned praise, yet reviewers warned that configuration files demand deep technical expertise and advised sticking to security upgrades to avoid breaking the system, with one recommending an experienced Asterisk expert stay on standby for serious telephone issues.

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