A method of maintaining cached Session Initiation Protocol (SIP) terminal capability information at an end user terminal of a telecommunication system, for one or more other end user terminals. The method comprises predefining one or more signalling message properties for signalling messages to be received from peer terminals, and recording the properties at said end user terminal, examining incoming signalling messages received from peer terminals to determine whether or not they possess a predefined property, and if an incoming signalling message does possess a predefined property, reacting by refreshing the cached capability information for the sending terminal.