Both siblings name the books that I would most likely to recommend. Also, Steve Call's "The Deal of the Century" and "Telephone: The First Hundred Years," John Brooks. The latter is a 1976 book which was commissioned by AT&T as a corporate history. As a result it is both outdated and paints a rather rosy picture[1], but I think that's part of what makes that book rather interesting - it's sort of AT&T's best version of itself at the peak of its dominance.

[1] for what it's worth, John Brooks engages right in the introduction with the conflict of a history funded by its subjects, and the book was researched and written independently

It’s mentioned below, but ‘The Idea Factory‘ covers Bell labs and is an excellent read.

The title is bad enough that I won't mention it, but the alternative title is good (and will find you the book):

'The Criminal Wrecking of the Best Telephone System in the World' by Kraus and Duerig.