This read-write value sets the caller category the Outgoing MFC register reports using the Mexican GroupII6 category list, which adds options like collect-call, time-and-charges, and three shared-line subscriber positions alongside normal-subscriber and maintenance-equipment. An admin configures this separately from the GroupII3 object because GroupII6 signaling defines its own, differently numbered set of caller categories the Incoming register may request. For example, an admin provisioning a party line would set this to subscriber2-on-shared-line (7) to identify the second subscriber position on that shared circuit.