Hello-Central is the very odd name of the daughter of Sandy and the Boss. We learn the child's name in chapter 40; in chapter 41, we find out why she has this name:
"The name of one who was dear to thee is here preserved, here made holy, and the music of it will abide alway in our ears. Now thou'lt kiss me, as knowing the name I have given the child."
But I didn't know it, all the same. I hadn't an idea in the world; but it would have been cruel to confess it and spoil her pretty game; so I never let on, but said:
"Yes, I know, sweetheart--how dear and good it is of you, too! But I want to hear these lips of yours, which are also mine, utter it first--then its music will be perfect."
Pleased to the marrow, she murmured:
"Hello, central" is an expression that Morgan (the Boss) sometimes uttered while sleeping, and Sandy thought it was the name of a woman he loved. She was almost right. It's not a name, but he was referring to an old girlfriend who happened to be a telephone operator. We know this from chapter 39. When the Boss is about to face Lancelot in the joust, he recalls: "Across my mind flitted the dear image of a certain hello-girl of West Hartford, and I wished she could see me now."