A voice or video call is to be established between a caller and a callee based on a call flow that involves a call establishment request and a corresponding call acceptance response. A first call establishment request is sent to a called terminal (of the callee) that is unready to accept the call upon receiving this first call establishment request. Once the called terminal is ready to accept the call, instead of the call acceptance response, a reverse call establishment request for the call is received back from the called terminal. The reverse call establishment request is automatically accepted on behalf of the caller on condition that the reverse call establishment request was received back from the called terminal within a certain time limit. If so, the call is accepted by sending an instance of the call acceptance response to called terminal.