Abstract: A method for routing communication calls via VoIP and via PSTN to communication devices and computer program products thereof A user (B) having a communication device (H) running an application (D) receives a communication call and upon the user (B) having decided, for a given data network, and before the call being received, which one of a VoIP or PSTN interface be preferred for receiving the call, the method comprising: if the VoIP interface is preferred, routing the communication call by a Communication Call Control Service (F) to the mobile communication application (D) as a VoIP call, and delaying the routing of the communication call over the PSTN interface; or if the PSTN interface is preferred, routing the communication call via the PSTN interface as a PSTN call, and if the result of the PSTN call indicates that said communication device (H) is not registered in the PSTN network further routing the communication call via the VoIP interface.