Archive.org has many phone related documents.
They have a lot of Bell System publications. I like the Bell Labs publication. You can find good 1-3 page articles.
Here is a Bell System search on archive.org :
https://archive.org/search.php?query=Bell%20System
If you come across good articles, please post them to the forum.
Jim
I like to search Paul F.'s site for bsp references on phones I am researching.
http://www.paul-f.com/
After I find the Bsp's numbers then I use the TCI Library
Here is the link for the TCI LIbrary:
https://www.telephonecollectors.info/
I also turn to the TCI Library for catalogs, marketing documents and other technical references.
Another favorite for vacations and idle time due to coronavirus is downloading and reading back issues of the club newsletters. Both TCI and ATCA have decades of monthly newsletters available on-line for members. Some amazing subjects have been documented. Partial index docs are available to whet your appetite.
https://www.telephonecollectors.org/ (https://www.telephonecollectors.org/)
https://www.telephonecollectors.org/JournalsSamples/Singing_Wires_Index.pdf (https://www.telephonecollectors.org/JournalsSamples/Singing_Wires_Index.pdf)
https://atcaonline.com/ (https://atcaonline.com/)
https://atcaonline.com/ATCANEWSIndex.htm
(https://atcaonline.com/ATCANEWSIndex.htm)
More BSPs are available here:
http://etler.com/bsp-archive/
http://bellsystempractices.org/ (http://bellsystempractices.org/)
Google books has back issues of telephony-related magazines and books.
Some other magazine archives are linked from the TCI Library:
https://www.telephonecollectors.info/index.php/browse/document-repository/catalogs-manuals/bell-system-we/bell-labs-record
https://www.telephonecollectors.info/index.php/browse/bstj-archive
(https://www.telephonecollectors.info/index.php/browse/bstj-archive)https://www.telephonecollectors.info/index.php/browse/document-repository/catalogs-manuals/lm-ericsson
(https://www.telephonecollectors.info/index.php/browse/document-repository/catalogs-manuals/lm-ericsson)
If you want to swat-up on British phones then Bob Freshwater's site is excellent - https://www.britishtelephones.com/
:)