While it has some technical details, it basically written in a light breezy style. It's more about the people themselves involved in phreaking than the specific techniques of how it was done; though the reader will get some idea of MF signalling tones and how the phreaks jumped in to take control.
It describes how developing the phreaking techniques took substantial patience and practice; one didn't just shoot off internal MF signals. The November
1960 BSTJ had a detailed article describing control and signalling over the network, and the early hackers made good use of this. But understanding this article requires a solid technical knowledge.
It describes some holes in the old Bell network that allowed the very determined phreaks to gain access to Verification trunks, allowing them to evesdrop on conversations, as well as access to the military's Autovon network.
The author provides a website loaded with documents.
Presumably, the replacement of 4A toll crossbar and the crossbar tandem, and the emergence of CCIS and SS7 eliminated the ability to hack into the network. But then we have modern hackers, like "Rachel from credit card services"