A network element of a communication provider arranged to receive a call invite from an originating end-user terminal inviting a destination end-user terminal to a proposed session for conducting a voice or video call over a packet-based network, in response to generate a push notification, and to send the push notification to the destination end-user terminal. The processing apparatus is configured to generate the push notification with a payload comprising call signalling information enabling a response regarding the proposed session to be formulated by the destination end-user terminal and returned to the originating end-user terminal, the call signalling information comprising at least (i) an indication that a session between end-user terminals is sought, and (ii) an identifier for responding to the originating end-user terminal.