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OpenSIPS vs Flexisip: catalog facts
OpenSIPS	Flexisip
Free Free and open source; paid training courses are offered separately.	Free Free under the AGPL 3.0, with a paid proprietary licence for closed-source use.
Linux, Self-hosted	Self-hosted
Handles high SIP traffic volumes Covers many roles from PBX to load balancer	Push gateway delivers calls and messages to mobile apps in the background Proxy, presence and B2BUA in one suite
Steep learning curve, aimed at telecom engineers Signaling server only, not an end-user calling app	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	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.