A voice or video call is established between the caller and the called party based on a call flow with a call establishment request and a corresponding call acceptance response. The first call establishment request is sent to the called terminal (the callee's) that is not ready to accept the call upon receipt of this first call establishment request. When the called terminal is ready to accept the call, instead of a call acceptance response, a reverse call establishment request for the call is received from the called terminal. The reverse call establishment request is automatically accepted on behalf of the caller provided that the reverse call establishment request is received from the called terminal within a specific time limit. In such case, the call is accepted by sending an instance of the call acceptance response to the called terminal. The called terminal is not ready when the client application for making the call is not installed on the called terminal. The client application is downloaded to initiate a return call as well as upon receiving the first call establishment.
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