Except as hereinafter provided, the corporate purpose of each cooperative formed hereunder shall be to render service to its members only, and no person shall become or remain a member unless such person uses telephone service supplied by the cooperative and shall have complied with the terms and conditions in respect to membership contained in the bylaws of the cooperative. Should the cooperative acquire any telephone facilities already dedicated or devoted to the public use it may, for the purpose of continuing existing service and avoiding hardship, continue to serve the persons served directly from such facilities at the time of such acquisition without requiring that such persons become members. The rates to such nonmembers shall be on a cost basis similar to those charged members.