enclosed is a copy of page #3 from a BSP and I thought you'd all like to know what the 300 series phones were originally designed for.
This is a great reference chart.
When posting BSP references, it's always helpful to include the issue number and date of the source BSP, for those who might want to read the entire document.
This page appears to come from C35.545 issue 1, March 1958, titled:
TELEPHONE SETS FOR INDOOR LOCATIONS--300 SERIES
IDENTIFICATION AND ASSEMBLY OF PARTS
.
It can be found using a simple search in the TCI Library or by this link:
http://www.telephonecollectors.info/index.php/document-repository/doc_details/4983-c38-545-i1-mar58-set-tel-300 (http://www.telephonecollectors.info/index.php/document-repository/doc_details/4983-c38-545-i1-mar58-set-tel-300)
Since other models may have been referenced in earlier or later BSPs, other sources should be consulted to get a complete picture of the evolution of the 300-series.
Some additional info has been summarized here:
http://www.paul-f.com/we300typ.htm (http://www.paul-f.com/we300typ.htm)
the reader would find that info out once the pull up the BSP in the library...