1. A method for establishing a real-time communication event between a user of a client device and another user of another client device via a communication network, the method comprising: performing a first phase of a communication event establishment procedure by transmitting via the network a message to the other client device or to a server connected to the network, the message including multiple options pertaining to a second phase of the communication event establishment process yet to be performed; wherein the message comprises, for each of the multiple options, a different network address unique to that option which can be accessed to select that option, and the method further comprises: detecting, via a notification from the server, which network address unique to one of the multiple options has been accessed by the other client device; and in response, instigating the second phase of the communication event establishment procedure in accordance with said one of the multiple options.