Don't Let Your Baby Suck the Telephone Cord!: May 1918
Not because it could hurt the baby, of course. But your little bundle of joy could short-circuit the telephone cord and interrupt Mrs. Henderson from next door while she's in the middle of delivering the hot gossip. In the early 20th century, PopSci reports that phone operators got several calls from distraught mothers confused as to why their connection was so spotty after Junior's teething session.