About Ostel

Ostel is a tool for having end-to-end encrypted phone calls. Our goal is to promote the use of free, open protocols, standards and software, to power end-to-end secure voice communications on mobile devices, as well as with desktop computers.

Client Applications


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We fully support and integrate with the CSipSimple app on Android. It has an OSTN setup wizard to make life easy. You'll only have to enter your name, password and ostel.co and you're ready to call!

iPhone & iPad

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Ostel works great on the Acrobits Softphone app. It's a paid app and for $6.99 you'll be able to receive encrypted calls. There's an additional $24.99 in-app purchase for the ZRTP extension to also place a secure call.


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The Jitsi app is an open source client that works for Ostel. It can also be used as a chat client for Facebook, GChat, XMPP and others.


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The Jitsi app is an open source client that works for Ostel. It can also be used as a chat client for Facebook, Gchat, XMPP and others.


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The sflphone app is a GPL app that works well with Ostel. The Jitsi app works too!


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Not to be forgotten, PrivateGSM works on Blackberry and even on Nokia. An enterprise solution, it requires payment to function fully.


The Guardian Project is a research and development effort powered by technology-focused activists, concerned citizen users, and open-source security software hackers. We build tools based on real-world experience and feedback. Our process is transparent, inclusive and responsible.

Documentation and source code for building your own service like ostel.co is available. We encourage anyone with Linux system skills to host their own backend to become part of a global federated secure VoIP network.

Open Secure Telephone Network (OSTN)

We are working to define a defacto standard called OSTN by which a voice over internet protocol service can be considered end-to-end secured, with verifiable encryption, minimal logging, and a decentralised model of deployment and use. From this standard, we will work to deploy a network of compliant server/service instances and client software, mobile and desktop, that are federated, audited and interoperable.

Call Your Friends For Free

Sign Up In 3 Easy Steps:

  1. Pick a name.
  2. Get the app.
  3. Start calling your Ostel friends.