Blue box (English Wikipedia)

Wozniak, Steve (October 17, 2007). iWoz: Computer Geek to Cult Icon. W. W. Norton & Company. p. 110. ISBN 9780393066869 – via Internet Archive. bluebox subculture.
Whipple Jr., Spencer (June 1, 1975). "Inside Ma Bell". 73. pp. 68–80. Retrieved May 9, 2019 – via Internet Archive.

books.google.com

Wilson, E. Jan (December 6, 1998). Telecom and Network Security: Toll Fraud & Telabuse Update. TRI-Telecommunications Reports International, Incorporated. ISBN 9780938866091 – via Google Books.
Gitlin, Martin; Goldstein, Margaret J. (December 6, 2015). Cyber Attack. Twenty-First Century Books. ISBN 9781467725125 – via Google Books.
Shinder, Debra Littlejohn; Cross, Michael (July 21, 2008). Scene of the Cybercrime. Elsevier. ISBN 9780080486994 – via Google Books.
LLC, New York Media (June 6, 1977). "New York Magazine". New York Media, LLC – via Google Books.
Pursell, Carroll W. (December 6, 2007). Technology in Postwar America: A History. Columbia University Press. ISBN 9780231123044 – via Google Books.

Breen, C.; Dahlbom, C. A. (1960), "Signaling Systems for Control of Telephone Switching" (PDF), Bell System Technical Journal, XXXIX (6): 1381–1444, doi:10.1002/j.1538-7305.1960.tb01611.x, The keyer relay M operates and releases from signals on the M lead and alternately removes or applies 2600 cycles to the transmit line of the facility. ... Table IV—Frequencies and Digit Codes for MF Pulsing: Digit 1: Frequencies 700 + 900 ...

Weaver, A.; Newell, N. A., "In-Band Single-Frequency Signaling" (PDF), Bell System Technical Journal

Breen, C.; Dahlbom, C. A. (1960), "Signaling Systems for Control of Telephone Switching" (PDF), Bell System Technical Journal, XXXIX (6): 1381–1444, doi:10.1002/j.1538-7305.1960.tb01611.x, The keyer relay M operates and releases from signals on the M lead and alternately removes or applies 2600 cycles to the transmit line of the facility. ... Table IV—Frequencies and Digit Codes for MF Pulsing: Digit 1: Frequencies 700 + 900 ...
Traffic Routing Guide, AT&T, 1977

Stix, Harriet (May 14, 1986). "A UC Berkeley Degree Is Now the Apple of Steve Wozniak's Eye". Los Angeles Times. Retrieved January 5, 2015.

UNITED STATES of America vs. Bernard CORNFIELD, dba Grayhall Inc, No. 76-3391, United States Court of Appeals, Ninth Circuit. October 27, 1977.