(4) The National Numbering Plan shall be consistent with the requirements of international agreements, commitments, conventions, regulations and recommendations to which Liberia has subscribed. (5) All service providers shall be required to use numbers assigned to them by the LTA in accordance with the National Numbering Plan and shall ensure that these numbers are used efficiently and in accordance with the National Numbering Plan. (6) Service providers shall also implement and maintain emergency service access and location identification services in accordance with any regulations, rules, orders or notices issued by the LTA. 63. Use of Numbers (1) Service providers and customers shall not have any property rights in numbers. (2) A Service Provider shall only change a customer’s number: (a) on request of the customer; (b) if a fixed service customer’s location changes; or (c) if it has reasonable grounds for doing so and if it has given reasonable advance written notice to the customer in question, stating the reason and anticipated date of change. In cases of emergency, oral notice with subsequent written confirmation shall be sufficient. 64. Number Portability (1) The LTA may, after consultation with the affected service providers and other interested parties, issue an order directing one or more service providers to develop or to assist in the development of a number portability implementation plan, for approval and implementation by order of the LTA. (2) In considering whether to implement number portability, the LTA shall have due regard to the costs of such portability, and the availability of technology that permits such portability in Liberia on a cost-effective basis. (3) The costs of introducing number portability systems and the ongoing costs of administering number portability shall be recovered from service providers in accordance with applicable rules or orders of the LTA. (4) No service provider, whether acting unilaterally or in collaboration with other service provider(s), shall offer number portability to any customer except in accordance with an implementation plan approved by the LTA, or as otherwise specifically approved by the LTA.