47 CFR § 52.5
Incumbent local exchange carrier. With respect to an area, an incumbent local exchange carrier is a local exchange carrier that:
(1) On February 8, 1996, provided telephone exchange service in such area; and
(i) On February 8, 1996, was deemed to be a member of the exchange carrier Association pursuant to § 69.601(b) of this chapter (47 CFR 69.601(b)); or
(ii) Is a person or entity that, on or after February 8, 1996, became a successor or assign of a member described in paragraph (a)(2)(i) of this section.