Single Line Set w/ Built in 4A?

[JB-Alert]

Hello everyone.  Looking for some help to find more information, and ideally the BSP, on the set below.  I recently won this on eBay.  It is in great condition (maybe NOS), with the spring and line cords new and original wrapping for the handset.  I connected to my test landline and it worked immediately (receiver and speakerphone).  Nice real bell, dials smoothly and the speakerphone has the same quality and functions as the 4A.  The button on the right, over the dial, is for 'Recall'.  The set is quite heavy, and the Speakerphone is 100 times better than the 'Telehelper' model.  The speakerphone has the same 4A legend, OFF / On or Quiet.  The base is marked model 960 C1M, and actually has a serial number, 110. 

Any help would be appreciated!