Note: The only system telephones in the group that are called are those which are available for a conversation, e.g. those that are not busy. This means the individual members of the group do not need to be logged into the group. They are still called if they are logged off from the group.
Note: For security reasons, the announcement is limited to 120 seconds to prevent possible misuse of this function (for example, eavesdropping from distant rooms).