The invention relates a method for providing a level of service for a Mobile Terminal (MT) in a packet data telecommunications network. The further method receives at the MT from a proxy server a request message for requesting the quality of service for a session between the MT and the proxy server. The method generates, based on a proxy server IP address received during a registration of the MT at the proxy server, a token for correlating accounting information and inform the proxy server of the quality of service to be applied to packet data sent on to be sent during the session, wherein the token includes the proxy server IP address and a session identity parameter and responsive to the reception of the request from the IMS proxy server, sending a response message including the token to the proxy server.