AT&T's 5ESS switch was a big deal to 1990s phone hackers.
 This is probably the best 5ESS textfile I've ever seen.
AT$T 5ESS(tm) From Top to Bottom by Firm G.R.A.S.P.
 On the Northern Telecom ("Nortel") DMS-100 switch
Understanding the Digital Multiplexing System Part One by Control C
Understanding the Digital Multiplexing System Part Two by Control C
Understanding the Digital Multiplexing System Part Two (B?) by Control C
Notes on using the DMS-100 Switching System Interface
 On Bell's COSMOS system
The Definitive COSMOS by Erik Bloodaxe
Computer System for Main Frame Operations (COSMOS) Part One by King Arthur
Computer System for Main Frame Operations (COSMOS) Part Two by King Arthur
 Other Bell System computer systems
Computer-Based Systems for Bell System Operations by Taran King 
Facility Assignment and Control Systems (FACS) by Phantom Phreaker
Loop Maintenance Operations System (LMOS) by Phantom Phreaker and Doom Prophet
The Fine Art of Telephony by Crimson Flash
 Added for the great descriptions of physically breaking into
 telephone company Central Office buildings, tapping SCCS lines, and more.
Everything a hacker needs to know about getting busted by the Feds by Agent Steal
 The document that finally gave me the "a-ha!" moment regarding the
 origin of the term "Recent Change" in switch parlance
Basic Concepts of Translation by The Dead Lord & The Chief Executive Officers
 Decent article on gaining access to other's phone lines via "junction boxes"
The Art of Junction Box Modeming by Mad Hacker
 On X.25 / Telenet / Tymnet / etc hacking
How We Got Rich Through Electronic Fund Transfers (EFTs) by The Legion of Doom
Hacking & Tymnet by Synthecide
BT Tymnet (1/3) by Toucan Jones
BT Tymnet (2/3) BT-GNS Worldwide Asynchronus Outdial Service by Toucan Jones
BT Tymnet (3/3) BT-GNS Worldwide Access Sorted By Node by Toucan Jones
Western Union Telex, TWX, and Time Service by Phone Phanatic
Everything you always wanted to know about Telenet Security ... by Phreak_Accident
Tymnet Support for Customer's Data Security by Tymnet
Telenet The Secret Exposed by Mad Max (cleaned up)
Telenet The Secret Exposed by Mad Max (original)
 LOD/H Technical Journal: Massive 3,000+ line text files
Issue 1 (1987)
Issue 2 (1987)
Issue 3 (1988)
Issue 4 (1990)
Issue 5 (1993)
 Phrack's reporting on Robert Tappan Morris's infamous Internet worm
A Report On The InterNet Worm by Bob Page
 The Hacker Crackdown: Law and Disorder on the Electronic Frontier
 By Bruce Sterling (1993)
The Hacker Crackdown (full book text)
 Mother Earth Mother Board
 By Neal Stephenson (1996)
Mother Earth Mother Board (full article text)
 Other textfiles
Metal Shop Private's Phreak/Hack Sub
Concerning Hackers Who Break into Computer Systems by Dorothy E. Denning
 On the OKI 900 phone and cellular cloning
The Complete Oki 900 guide by IceBerg
 The alt.2600/#hack FAQ
 The alt.2600/#hack FAQ by Voyager (beta .013 / 1996)
 "International Subversive": 1990s Australian hacking scene, "Underground" book, old school Julian Assange, etc
Internationl Subversive Volume #1, Issue #1, 1991-08-21
 Textfile archives / mirrors
Phrack Archive