S.C. Code Ann. § 58-9-250

No telephone utility shall, as to rates or services, make or grant any unreasonable preference or advantage to any person or corporation or subject any person or corporation to any unreasonable prejudice or disadvantage. No telephone utility shall establish or maintain any unreasonable difference as to rates or service, either as between localities or as between classes of service. Subject to the approval of the Commission, however, telephone utilities may establish classifications of rates and services and such classifications may take into account the conditions and circumstances surrounding the service, such as the time when used, the purpose for which used, the demand upon plant facilities, the value of the service rendered or any other reasonable consideration. The Commission may determine any question arising under this section.