In a system of the type in which for call setup each circuit segment is selected from available circuit segments, at least one circuit segment is permanently reserved on each trunk between nodes needed to set up circuits for particular calls to or from preferred users, and circuit segments are dynamically allocated from the reserved segments for setting up a circuit from the terminal of one user who has a preferred user attribute for particular calls in the event of a call set-up request by one of the users in respect of a call for which he has been granted a preferred user attribute.