“Competitive Telecommunications Service” means a telecommunications service, its functional equivalent or a substitute service, which, for some identifiable class or group of customers in an exchange, group of exchanges, or some other clearly defined geographical area, is reasonably available from more than one provider, whether or not such provider is a telecommunications carrier subject to regulation under this Act. A telecommunications service may be competitive for the entire state, some geographical area therein, including an exchange or set of exchanges, or for a specific customer or class or group of customers, but only to the extent consistent with this definition.