The rule to show cause provided for in § 49-9-40 shall be directed to the interested persons who have furnished the company the written statement or request prescribed in § 49-9-10 and shall be personally served upon such persons as are residents of the State. If the persons to be served are nonresidents service may be made by registered mail, in which case a copy of the rule and petition shall be mailed at least ten days prior to the return date of such rule.