A method of modifying a call setup message for a call from a first terminal to a second terminal, the call setup message being sent from the first terminal to a network node via an intermediate node which handles at least some signaling or traffic associated with the call, wherein the network node is responsible for negotiating call setup requirements for the call to the second terminal, the method comprising the steps of: intercepting the call setup message at the intermediate node; identifying one or more preferences or capabilities associated with the intermediate node which may impact the way in which the intermediate node can handle signaling or traffic associated with the call; modifying the call setup message based on information relating to said preferences or capabilities; and sending the modified call setup message to the network node, in order that the node can effect said negotiations based on the modified message.