When Love Calls — Stanley J. Weyman

Hannah Gregory is good at many things, but that list doesn't include following rules. So when she is forced to apply for a job as a telephone switchboard operator to support her two sisters, she knows it won't be easy. "Hello Girls" must conduct themselves according to strict--and often bewildering rules. No talking to the other girls. No chatting with callers. No blowing your nose without first raising your hand. And absolutely no consorting with gentlemen while in training.