Voice Calling

Voice calling with Android Voice and Video SDK. Set up calling between applications, from application to phone, app to SIP and conference calls. Get more information here.

The Sinch SDK supports four types of calls: app-to-app (audio or video), app-to-phone, app-to-sip and conference calls. The CallController is the entry point for the calling functionality of the Sinch SDK.

Calls are placed through the CallController and events are received using the CallControllerListener. The call controller is owned by the SinchClient and accessed using sinchClient.callController.

Set Up an App-to-App Call

Use the CallController.callUser() to the call method, so that Sinch services can connect the call to the callee.

val callController = sinchClient.callController
val call = callController.callUser("<remote user id>", new MediaConstraints(false))
// Or for video call: val call = callController.callUser("<remote user id>", new MediaConstraints(true))

A call object is returned, containing details about the participants in the call, call details such as start time, call state and possible errors.

Assuming the callee’s device is available, the CallListener.onCallProgressing() is called. It notifies the application that the outgoing call is progressing. If a progress tone should be played, this is where it should be started.

When the other party answers, the CallListener.onCallEstablished() is called. Now, the users can start talking. If a progress tone was previously played, it should be stopped now.

Set Up an App-to-Phone Call

An app-to-phone call is a call that's made to a phone on the regular telephone network. Setting up an app-to-phone call is not much different than setting up an app-to-app call.

Instead of invoking the callUser method, invoke the CallController.callPhoneNumber(). The phone number also should be specified to the E.164 number formatting standard and should be prefixed with a ‘+’.

Example: To call the US phone number 415 555 0101, the phone number should be specified as +14155550101. The ‘+’ is the required prefix and the US country code ‘1’ prepended to the local subscriber number.

Presenting a number to the destination you are calling

Mandatory step!

You must provide a CLI (Calling Line Identifier) or your call will fail.

You need a number from Sinch so you can provide a valid CLI to the handset you are calling. If you have a trial account, you can use the test number that is available for free. If you have already upgraded your account, you can purchase a number to use on the dashboard.


When your account is in trial mode, you can only call your verified numbers. If you want to call any number, you need to upgrade your account!

Credits Required

Remember, placing an App-to-Phone call requires that your Sinch account has sufficient credits. Add credits on your Account page. Credits are used each time an App-to-Phone call is placed and your account balance is updated after each call.

// Instantiate an app to phone call using the CallController.
val callController = sinchClient.callController
// If you're on trial account you have to register the destination number first. See https://dashboard.sinch.com/numbers/verified-numbers
val destinationNumber = "<one of your verified numbers>"
// You can either use a test number https://community.sinch.com/t5/Virtual-Numbers/How-can-I-activate-my-free-number-for-testing/ta-p/8578 or purchase one here:
// https://dashboard.sinch.com/numbers/your-numbers
val cli = "<test or purchased cli number>"
val call = callController.callPhoneNumber(destinationNumber, cli)
Testing DTMF

In an App-to-Phone scenario, it's possible to issue DTMF sequences using the Sinch SDK. Note that if the receiving end of the call is an iOS device, you might have to disable VoLTE ("Voice over LTE") option in the settings of the phone at the receiving end of the call in order to be able to hear DTMF tones.

Set Up an App-to-sip Call

An app-to-sip call is a call that's made to a SIP server. Setting up an app-to-sip call is not much different from setting up an app-to-app call. Instead of invoking the callUser method, invoke the CallClient.callSip(). The SIP identity should be in the form <user@server>. By convention, when passing custom headers in the SIP call, the headers should be prefixed with x-. If the SIP server reported any errors, the CallDetails object will provide an error with the SIP error type.

Set Up a Conference Call

A conference call can be made to connect a user to a conference room where multiple users can be connected at the same time. The identifier for a conference room may not be longer than 64 characters.

val callController = sinchClient.callController
val call = callController.callConference("<conferenceId>")

it's also possible to connect users to a conference call via the Sinch REST API.

Handle Incoming Calls

To answer calls, the application must be notified when the user receives an incoming call.

Add a CallControllerListener to the CallController to act on the incoming calls. As calls come into device CallControllerListener.onIncomingCall() will be executed.

val callController = sinchClient.callController

When the incoming call method is executed, the call can either be connected automatically without any user action, or it can wait for the user to press the answer or the hangup button. If the call is set up to wait for a user response, we recommended that a ringtone is played to notify the user that there is an incoming call.

override fun onIncomingCall(callController: CallController, call: Call) {
    // Start playing ringing tone

    // Add call listener

To get events related to the call, add a call listener. The call object contains details about participants, start time, potential error codes, and error messages.

Incoming video call

When an incoming call is a video call, the CallControllerListener.onIncomingCall() is also executed with isVideoOffered flag returning true. See video calling section for details how to handle video views.

Answer incoming call

To answer the call, use the Call.answer() method on the call to accept it. If a ringtone was previously played, it should be stopped now.

User presses the answer button:

// User answers the call

// Stop playing ringing tone

Now, the clients on both ends establish the connection. When the call is established and the voice streams are running in both directions, the CallListener.onCallEstablished() is called.

Decline incoming call

If the call shouldn't be answered, use the Call.hangup() on the call to decline. The caller is notified that the incoming call was denied. If a ringtone was previously played, it should be stopped now.

User presses the hangup button:

// User doesn't want to answer

// Stop playing ringing tone

Disconnecting a Call

When the user wants to disconnect an ongoing call, use the Call.hangup() method. Either user taking part in a call can disconnect it.

Hanging up a call:


When either party disconnects a call, the application is notified using the call listener method CallListener.onCallEnded(). This allows the user interface to be updated, an alert tone to be played or similar actions to occur.

A call can be disconnected before it has been completely established.

Hanging up a connecting call:

// Starts a call asynchronously
val call = callClient.callUser("<remote user id>")

// User changed his/her mind, let’s hangup

Volume Control

To make sure that the volume of the call can be modified by the hardware volume controls, setVolumeControlStream(AudioManager.STREAM_VOICE_CALL) must be called on the Activity where the call is handled. Make sure that volumeControlStream is reset to a suitable value when the call has ended.

For example, after creating a call (using CallClient.callUser();`.

When the call ends, set the volume control stream back to it’s previous value. For example in your implementation of CallListener:

override fun onCallEnded(call: Call) {

Audio Routing

AudioController interface allows you to control audio routing. Aquire AudioController using SinchClient.audioController, and use following methods:

Method Description
mute() Mutes audio input.
unmute() Unmutes audio input.
enableSpeaker() Enables speaker mode.
disableSpeaker() Disables speaker mode.
enableAutomaticAudioRouting() Enables automatic audio (AAR).
disableAutomaticAudioRouting() Disables automatic audio routing (AAR).

Automatic audio routing

You can enable automatic audio routing using AudioController.enableAutomaticAudioRouting(). It enables automatic audio routing between earpiece, speakerphone, wired headset and Bluetooth audio devices.

It takes single AudioController.AudioRoutingConfig parameter that allows you to specify:

  • boolean manageBluetoothAudio if set to true, allows to automatically reroute audio to Bluetooth headset when available. Fires MissingPermissionException if android.Manifest.permission.BLUETOOTH is not granted.
  • AudioController.UseSpeakerphone useSpeakerphone can be set to AUTO , TRUE or FALSE . The AUTO mode uses a proximity sensor to operate.

Priorities are following:

  • Bluetooth (if available and manageBluetoothAudio == true)
  • Wired Headset
  • Default audio device if useSpeakerphone is TRUE or FALSE ; or Proximity sensor's based decision (speakerphone / earpiece) if useSpeakerphone is AUTO .

Default audio device (speakerphone/ earpiece) is set using useSpeakerphone parameter.

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