Fifty years ago, the hit TV show "Laugh In" premiered.
One running sketch was the parody of a telephone operator/ service representative known as Ernestine, played by Lily Tomlin.
An article about Laugh In includes mention of this sketch:
As an aside, telephone operators were frequent mocked because they did have a peculiar way of speaking. For instance, to say "nine", they'd say "NI-EN--Strong N, a long I, and a mild emphasis on EN." But this was done intentionally since early telephone lines weren't that clear and the Bell System wanted to avoid errors as telephone numbers were passed along from one operator to another. Further, the Bell System was heavily standardized in work procedures and everyone in cities were trained the same way.
Page 9 of the following operator's manual has the guide: