Rachael Morrison and her team poured their heart into this and it shows... it is just so good. (Disclaimer: I was interviewed for the movie and narrate parts of it.) See it if you can.
Rachael Morrison, the director, was kind enough to invite me to the premier at Sundance, since she interviewed me for the film. She and her crew did an amazing job. She found so much archival material and she and her team stitched it together to tell a moving and historically accurate story. People were in tears after the premier. Just so good.
* (Shameless plug) My book on the history of phone phreaking, Exploding the Phone, which has a lot of stuff on Engressia in it: https://explodingthephone.com/
Evan's stuff is excellent and worth watching/listening to.
Shameless plug: if you like his stuff, you might also like my book, "Exploding The Phone", which is a history of phone phreaking. https://explodingthephone.com/
SS5 was derived from AT&T's US MF signaling system, described in "Signaling Systems for Control of Telephone Switching" by Breen and Dahlbom, Bell System Technical Journal, November 1960. PDF here: https://explodingthephone.com/hoppdocs/breen1960.pdf
The BSTJ article has a discussion on international signaling on pp. 1430-1441.
Yes! This is what I concluded when, a few years back, I did a similar analysis to what matthiasl posted. <shameless plug> If you're interested in this kind of thing, please check out my book, Exploding the Phone. https://explodingthephone.com </shameless plug>
Someone mentioned phrack above. There was (still is!) also 2600, and before that, YIPL/TAP, the original phone phreak newsletter: https://archive.org/details/YIPLTAP_1-91
If you want something really ancient, check out YIPL/TAP, which was the first phone phreak newsletter (started publishing in May 1971) that was the granddaddy of 2600. You can get it on the Internet Archive: https://archive.org/details/YIPLTAP_1-91
That's a very kind question, thanks! In terms of what I get in the end, it doesn't really matter where you buy it (e.g., Amazon, local bookstore, whatever), although I'd love it if you supported your local bookstore -- they need help! Format matters a bit more in terms of royalty percentage (I get a higher percentage on ebooks)but ebooks also are priced lower, so the net to me between paperback and ebook is not much different.
Author of Exploding The Phone here, thanks for the mention and glad you enjoyed it! One thing I did that I'm pretty proud of is that I put almost all the research documents that I dug up (FOIA, newspaper articles, etc.) up on my website, where you can dig through them. E.g.: http://explodingthephone.com/search.php?q=blue+box&sort=rele... (please pardon the lack of https!) And to the other commenter about Evan Doorbell's excellent tapes about phone phreaking: I was lucky enough to get Evan to narrate the Audible version of my book!