The invention relates to a method of registering a communication client at a communication server, wherein the communication client is associated to a mobile terminal and wherein the communication server is associated to a mobile switching node of a circuit switched network, the method comprises the steps of: initiation a connection between the communication server and the communication client, sending identification information to the communication server by the communication client via the connection, interrogating an authentication module of the mobile switching node to perform a user authentication by the communication server, fetching subscriber information from a database by the communication server, and sending subscriber information to the communication client via the connection.