After commencement of the action, any party may take the testimony of any person, including a party, by deposition upon oral examination. Leave of court, granted with or without notice, must be obtained only if the plaintiff seeks to take a deposition prior to the expiration of 30 days after service of the summons upon any defendant, except that leave is not required (a) if a defendant has served a notice of taking deposition or otherwise sought discovery, or (b) if special notice is given as provided in Rule 30.02(2). The attendance of witnesses may be compelled by subpoena as provided in Rule 45. The deposition of a person confined in prison may be taken only by leave of court on such terms as the court prescribes.