## App to App calls

Apps can call other apps using the iOS, Android or Javascript SDK. Both call legs are established over the data connection of the smartphone or computer (VoIP). For additional call control, you can specify a callback URL where Sinch will send call-related events. By capturing and responding to these events from your app you can allow, deny, and control the calls. You can configure the callback URL under your app's voice settings in the Sinch [dashboard](https://dashboard.sinch.com/voice/apps).

For more information please check the [Callback API](https://developers.sinch.com/docs/voice/api-reference/voice/callbacks/). The callback event that's used in app to app calls is the *Incoming Call Event* callback.