Mont. Code Ann. § 25-3-402

Subject to the provisions of Rule 5(b), M.R.Civ.P., whenever a plaintiff or a defendant who has appeared resides out of this state and has no attorney in the action or proceeding, service may be made on the clerk of court for that party. However, in all cases in which a party has an attorney in the action or proceeding, the service of papers, when required, must be upon the attorney instead of the party, except of subpoenas, writs, and other process issued in the suit and papers to bring the party into contempt, unless the court orders otherwise.