Mo. Rev. Stat. § 392.150: Employees to notify sender when message cannot be transmitted immediately — penalty.

In all cases where application is made to any telephone or telegraph company, or the operator, agent, clerk or servant thereof, to send a dispatch, it shall be the duty of such operator, agent, clerk or servant who may receive dispatches at that station, plainly to inform the applicant, and, if required by him, to write upon the dispatch that the line is not in working order, or that the dispatches already on hand for transmission will occupy the time so that the dispatch offered cannot be transmitted within the time required, or promptly, if the facts be so; and for omitting so to do, or for intentionally giving false information to the applicant in relation to the time within which the dispatch offered may be sent, such operator, agent, clerk or servant, and the company by which he is employed, shall incur a like penalty as in section 392.130.