Pen register means a device which records or decodes electronic or other impulses which identify the numbers dialed or otherwise transmitted on the telephone line to which such device is attached but does not include (1) any device used by a provider or customer of an electronic communication service for billing or recording as an incident to billing for communication service provided by such provider or (2) any device used by a provider or customer of an electronic communication service for cost accounting or other like purposes in the ordinary course of its business.