Iowa Code § 477.8: Negligence presumed.

In any action against any telegraph or telephone company for damages caused by erroneous transmission of a message, or by unreasonable delay in delivery of a message, negligence on the part of the telegraph or telephone company shall be presumed upon proof of erroneous transmission or of unreasonable delay in delivery, and the burden of proof that such error or delay was not due to negligence upon its part shall rest upon such company.