No utility shall abandon all or any portion of its facilities subject to the jurisdiction of the commission, or any service rendered by means of such facilities, without first obtaining the permission and approval of the commission. The commission shall grant such permission and approval, after notice and hearing, upon finding that the continuation of service is unwarranted or that the present and future public convenience and necessity do not otherwise require the continuation of the service or use of the facility; provided, however, that ordinary discontinuance of service or use of facilities for nonpayment of charges, nonuser or other reasons in the usual course of business shall not be considered as abandonment. In considering the present and future public convenience and necessity, the commission shall specifically consider the impact of the proposed abandonment of service on all consumers served in this state, directly or indirectly, by the facilities sought to be abandoned.