A new area code will be introduced to overlay existing NPA 918 covering the eastern part of Oklahoma (Broken Arrow, McAlester, Tulsa). The new NPA 539 will become active on April 1, 2011. The permissive 10 digit dialing period for area code 918 was introduced on August 7, 2010. Mandatory 10 digit dialing will be activated on March 5, 2011.
See NANPA announcement and map of new overlay complex 539/918 (PDF document)