A network element of a communication provider comprising: transceiver apparatus 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; and processing apparatus configured to generate a push notification in response to the call invite from the originating end-user terminal; wherein the transceiver apparatus is arranged to send the push notification to the destination end-user terminal; wherein the processing apparatus is configured to generate the push notification with a payload comprising session establishment information enabling a call acceptance response regarding the proposed session to be formulated by the destination end-user terminal and returned to the originating end-user terminal, the session establishment information comprising at least an indication that a session between the said end-user terminals is sought, and an identifier for responding to the originating end-user terminal; wherein the call acceptance response is returned from the destination end-user terminal to the originating end-user terminal without being sent via a network element of the communication provider; wherein the identifier comprises one or both of a username of a user of the originating terminal, and an address of the originating end-user terminal, and wherein one or both of the address and username are not included in the call invite from the originating end-user terminal, and the processing apparatus of said network element is configured to resolve the address and/or username in response to the call invite and add the address and/or username into the payload of the push notification. transceiver apparatus 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; and processing apparatus configured to generate a push notification in response to the call invite from the originating end-user terminal; wherein the transceiver apparatus is arranged to send the push notification to the destination end-user terminal; wherein the processing apparatus is configured to generate the push notification with a payload comprising session establishment information enabling a call acceptance response regarding the proposed session to be formulated by the destination end-user terminal and returned to the originating end-user terminal, the session establishment information comprising at least an indication that a session between the said end-user terminals is sought, and an identifier for responding to the originating end-user terminal; wherein the call acceptance response is returned from the destination end-user terminal to the originating end-user terminal without being sent via a network element of the communication provider; wherein the identifier comprises one or both of a username of a user of the originating terminal, and an address of the originating end-user terminal, and wherein one or both of the address and username are not included in the call invite from the originating end-user terminal, and the processing apparatus of said network element is configured to resolve the address and/or username in response to the call invite and add the address and/or username into the payload of the push notification.