The present invention relates to a method and system for modifying at least one connection parameter of a circuit switched terminal device, wherein the at least one connection parameter can be modified at a called terminal by a corresponding input operation after the receipt of a setup signaling message. The connection parameter is incorporated in an answer signaling message to be transmitted in response to the setup message, and compared with a negotiated connection parameter. Based on the comparison result, a parameter modification is initiated. Thereby, a discreet and fast slip from an offered to a wanted service can be offered at little message traffic.