Any investigation, inquiry or hearing which the Commission has power to undertake or hold, except matters pertaining to rate changes, may be undertaken or held by or before any one or more of the commissioners, upon condition, however, that such commissioner or commissioners shall have been authorized by the Commission to undertake or hold such investigation, inquiry or hearing. Each investigation, inquiry or hearing before or by any such commissioner or commissioners shall be deemed to be the investigation, inquiry or hearing of the Commission. Any determination, ruling or order of a commissioner or commissioners, upon any such investigation, inquiry or hearing undertaken or held by him or them shall not become effective until due notice has been given to the Commission and it has been approved and confirmed by at least a quorum of the Commission and ordered to be filed in its office and any such determination, ruling or order involving the fixing or regulation of a general schedule of rates shall not become effective until due notice has been given the telephone utility concerned and an opportunity has been given such utility to be heard before, and the determination, ruling or order has been approved and confirmed by, at least a quorum of the Commission. Upon such confirmation and order, such determination, ruling or order shall be the determination, ruling or order of the Commission.