No telephone company shall hereafter begin the construction or operation of any telephone plant or system or of any extension thereof, for the purpose of furnishing public utility telephone service, without first obtaining from the commission a certificate that public convenience and necessity requires or will require such construction or operation of the plant or system; provided, that this section shall not apply to:

A. construction of plant or system within a certificated area which such telephone company already lawfully serves, where such construction is necessary in the ordinary course of business;

B. extension of plant or system to area contiguous to the certificated area of such telephone company, if such contiguous areas are not certificated and are not receiving public utility telephone service from another telephone company; provided that the commission shall be notified, in such manner as it may prescribe by rule, of any such extension into contiguous area; and

C. such construction or extension occurring when a proper application is being made pursuant to Section 4 [63-9-4 N.M. Stat. Ann.] of this act.