Standardization Sector of the International Telecommunication Union (ITU-T). Approved on 11 May 2006. Recommendation E–Series: Overall Network Operation, Telephone Servuce, Service Operation and Human Factors. 16 p. Telecommunication charge cards may be issued by Operating Agencies (OAs) to allow customers to use their card in connection with various international services at appropriate charges for each transaction and have the charges billed to their account in the country where the OA issued the charge card. Cards issued by OAs in accordance with this Recommendation conform to the appropriate ISO Standards