Section 12C. Any radio utility operating under a certificate issued by the department shall be subject to the jurisdiction of the department in the same manner and to the same extent as are common carriers; provided, however, that the department may allow a rate for a radio utility to fluctuate below a maximum rate; and provided, further, that any such rate below the maximum shall become effective only after notice is provided to the customers of such utility, and upon such radio utility filing a notice thereof with the department at least twenty-four hours prior to any such change. The department may establish rules and regulations necessary to carry out the provisions of this section.