In this subdivision:
I. "Number retention" means the ability of a telephone service customer to retain that customer's direct inward dialing telephone number at the same location, or a different location served by the central office that provides private branch exchange service to the shared tenant services provider, when switching service providers.
II. "Private branch exchange" means a telephone switch that can switch voice and data communications among the users of such switch, to the local telephone utility's central office or directly to inter-exchange carriers.
III. "Shared tenant services" means voice and data communications services under which tenants at a single building, business park, office park, or mall are provided with such services through a private branch exchange.