Cooperative, nonprofit, membership corporations may be organized under this chapter for the purpose of furnishing telephone service in rural areas to the widest practical number of users of such service; provided, that there shall be no duplication of service where reasonably adequate telephone service is available. Corporations organized under this chapter and corporations which become subject to this chapter in the manner provided in this chapter are referred to in this chapter as “cooperatives,” and shall be deemed to be not-for-profit corporations.