100. Telephone utility shall provide full metallic circuits or equivalent for all subscribers located within the base rate area and insofar as economically feasible to all rural multi-party subscribers located beyond the base rate area. Telephone utilities operating ground return rural circuits, which are affected by inductive interference, should cooperate to the fullest extent possible with all interested parties in correcting this condition and, where necessary to eliminate inductive interference, full metallic or equivalent circuits properly transposed shall be provided by the company at its own expense