A method of setting operating data is provided wherein a display, at a predetermined key telephone set, indicates the capabilities of all sets of the system to perform the various functions of which the system's key telephones are capable. The display indicates three conditions: whether all telephones are capable of performing the indicated function, whether no telephones are capable of performing the function, or whether at least one but not all telephones are so capable. The setting of operating data is facilitated by this display. Changes made in operating data are not permanent until a setting key is depressed. Before that, the original operating data may be recovered.