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Kamailio vs Flexisip: catalog facts
Kamailio	Flexisip
Free Free and open source under the GPLv2 or later.	Free Free under the AGPL 3.0, with a paid proprietary licence for closed-source use.
Linux, Self-hosted	Self-hosted
Handles thousands of call setups per second WebSocket support for WebRTC plus TLS for secure signalling	Push gateway delivers calls and messages to mobile apps in the background Proxy, presence and B2BUA in one suite
Infrastructure for engineers, not an end-user calling app Configuration requires solid SIP and VoIP knowledge	Requires SIP and VoIP knowledge to deploy Conference server is now a separate package
Downloadable app, Self-hosted	Self-hosted
Open source	Open source
License: GPL-2.0-or-later	License: AGPL-3.0
No account needed	Not stated if an account is needed
Not stated if it works offline	Not stated if it works offline
Official website Full listing and sources Checked October 2, 2026	Official website Full listing and sources Checked October 2, 2026

Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.