Frequently Asked Questions

OStel is a public testbed of the Open Secure Telephony Network (OSTN) project, an effort with the goal of promoting 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. Both are concepts from The Guardian Project.

How do I set it up?

Register for an account. Then download the app and enter the username and password of your ostel account to get started. The server name is "". A list of compatible apps is listed on your account profile page and in the welcome email.

How do I test that everything is working?

From the dial pad, dial 9196 then click the green receiver icon at the bottom. Speak into the microphone. You should hear yourself. If so, you have successfully completed the echo test and your client should be fully functional.

How do I call my friends

Your friends need an ostel account too. To ensure your call security, ostel service cannot make calls to land lines or SIM card phone numbers on cellular networks. In the CSipSimple app, click 'txt' to type in your friend's user name and click the phone icon to place the call. See? Wasn't that easy?

Does ostel work on my mobile device or desktop?

Yes and yes! OStel works on every smartphone (Blackberry, iPhone, Nokia, Android) and every desktop (Mac, PC, Linux, etc) through accompanying apps that support SIP and ZRTP. Check out our features page for instructions to get it up and running on your platform.

I didn't get a confirmation email. What happened?

Check your spam box for an email from If you forgot your password, you can reset it here.

What kind of encryption do you use?

Phone calls with Ostel are end-to-end encrypted using ZRTP & SRTP. Each phone client has its own cipher strength options. We use SIP over TLS for signaling encryption. The TLS certifcates are based on the standard Root CA trust model.

Can I call landlines from Ostel and have it encrypted?

Unfortunately, no. Our open secure telephony network (OSTN) doesn't communicate with the public switched telephone network (PSTN). If it did, all land lines would basically have to subscribe to that same service to receive secure calls.

Error while registering - Forbidden. What happened?

Please check that there are no extra spaces in any of the fields you were meant to alter. Check that all spelling is using lowercase.

Error while registering - Bad Gateway. What happened?

Please make sure that your account information is correct by logging into the web site. If the problem persists, restart the app and try again.

I changed my settings but I'm getting the same error.

Try to exit the application and restart it. Click "Back" until you read the dial pad. Click "Settings" to reveal the options Menu. Click "Disconnect" to exit the app completely. Launch the app again from the applications folder and it will reboot and try to connect using the new settings you entered.

My connection is now inactive. What happened?

Are you trying to connect over a 3G/4G connection? Please try wifi. If this happens repeatedly, please notify us via the support email at and we will look into it.

I'm running Cyanogen. Why isn't OStel working?

Good question. It should. We're looking into some reported problems with CSipSimple and Cyanogen.

Can someone record my phone calls?

No one but you and the person you are speaking to can record calls placed on ostel if you've verified the ZRTP code.

Is ZRTP encryption working if no 4 digit number pops up?

If you don't see a short authentication srting (SAS) ZRTP confirmation code, it is not active and you're not encrypted.

Are you logging any data?

We only log information required to operate the service. We log this data securely and privately. Check out our privacy policy for full details.

Can I make video calls?

Yes! This is a feature we're currently debugging. Stay tuned for secure video calls!

Does this work with other SIP providers?

Yes. Any SIP server that uses secure signaling (sip-tls) over port 5061 can call

Can I delete my account?

Sort of. Since ostel doesn't require any information associated with your identity other than an email address, you can click the "Change account settings" link on your user page and change your email/password/username to anything not resembling you.

Can my username be in a language other than English?

Unfortunately we don't support this since it makes it easier to spoof accounts through impersonation. We hope to in the future.

I'm running Orbot. Why isn't OStel working?

No Voice over IP services work over a Tor connection due the limitations of the Tor network and VoIP protocols. Please turn off Orbot when running OStel if you've enabled transparent proxying. There are more details over on our blog.

My phone won't allow me to install the CSipSimple App.

Don't want to use the Google Play store? Enable your phone to install apps from 3rd parties then get it directly. Go to Settings then click on Applications. Under Unknown sources, make sure that the box is checked, allowing the installation of non-Market applications.

Does Ostel support text messaging?

Sort of. It works, but messages are only encrypted between the device/app and the server. This means they are more secure than SMS or plain email, especially since we don't log, but they are not encrypted end-to-end. We hope to enable OTR encryption for messages soon, but in the meantime, you can use our Gibberbot app on Android for end-to-end encrypted messaging.

Where are your servers located?

The server is located at Open Hosting, a privacy-friendly provider in the USA. World wide points of presence are under construction. Remember there are no stored call records, each authenticated call uses unbreakable encryption and there are no back doors for authorities.

What are the technical details on Ostel & the Open Secure Telephony Network (OSTN)?

Happy to share! Check out the full details about our software and hardware on our wiki at Open Secure Telephony Network (OSTN).

How do I set up Ostel on an Android?

You'll have to have the CSipSimple app and add your Ostel account information. Check out the full details about it on our wiki at CSipSimple. Please note that the nightly releases may or may not be stable if you get the app directly from their site.

How do I set up Ostel on an iPhone or iPad?

You'll have to have the Acrobits or Groundwire app and add your Ostel account information. Check out the full details about it on our wiki at Groundwire. Please note that there isn't a free or open source client for iOS yet and this version costs money.

How do I set up Ostel on Linux or Windows?

You'll have to have the Jitsi app and add your Ostel account information. Check out the full details about it on our wiki at Jitsi.

How do I set up Ostel on Blackberry or Nokia?

You'll have to have the PrivateGSM app and add your Ostel account information. Check out the full details about it on our wiki at PrivateGSM.

I had an account on Do I have one on

Nope! Our project is opt-in only to keep our users nice and happy.

It looks like everything is configured properly, so why is it still not working?

We're finding that some Internet Service Providers block all secure SIP traffic. Check out this post by our lead engineer Check out the full details about it on our wiki at CENSORSHIP.

My problems aren't listed here. Can I get in touch with someone?

We're always happy to help! Send us an email and we'll help troubleshoot your issue.

How can I get my friends involved?

We're always looking for smart and passionate people. Ask them to sign up for an account or follow us on Twitter or read our Blog for more information!

My problems aren't listed here. Can I get in touch with someone?

We're always happy to help! Send us an email to and we'll help troubleshoot your issue.


If you have any questions or concerns, please email You can also submit issues and bug reports in our project tracker. Our code is publicly available on Github.