On Tuesday, June 24, 2014 12:42:33 PM UTC-4, Stephen Sprunk wrote:   
      
   > It's hard to provide a precise list since it varied by vendor.  Some   
   > analog PBXes did have some advanced features, such as forwarding,   
   > transfer or 3-way calling, accessible by dialing special feature codes   
   > or using hookflash--and many of those eventually appeared on home phone   
   > lines as well, as premium options.   
      
   All of those features existed in PBXs since the beginning--they were merely   
   handled the by the PBX attendant*.  The challenge was to automate those   
   features, especially on direct-inward-dialing where the attendant didn't   
   figure into the call.  Some    
   features came out in the 1960s, like 'camp-on'.   
      
   I believe the basic features you mention were available on early generation   
   electronic switches, definitely by the early 1970s.  Transfer and 3-way   
   calling didn't need any special code; the person merely flashed the   
   hookswitch, got a second dial tone,    
   and dialed the next number.   
      
   FWIW, here is a description of a Bell System PBX from 1975.  It gives an idea   
   of what features were available, and what work was necessary 'behind the   
   scenes' to provide them:   
   http://www.telephonecollectors.info/index.php/document-repositor   
   /doc_details/11702-75may-blr-p243-770a-pbx-new-features   
      
   In 1976 Bell developed new custom features for its Dimension PBX, these   
   additional features required special electronic telephone sets.  I'm not sure   
   if they were "digital" in the sense you described it.  I suspect this was a   
   premium service--in those    
   years, most offices had more conventional PBX equipment, this sort of   
   equipment was found in places like a high-end law firm.   
   http://www.telephonecollectors.info/index.php/document-repositor   
   /doc_details/11723-76nov-blr-p274-dimension-custom-service   
      
      
   More sophisticated features were available, but did require dialing a special   
   code.  As you said, many users did not know how to use them unless it was a   
   routine part of their job.  Heck, today many people don't even know how to   
   transfer a call.     
      
      
      
   * In the old days, on a PBX, flashing the hookswitch would signal the   
   attendant to enter the call.  On basic systems, it was necessary to keep   
   flashing until the attendant answered, on fancier ones, only a single flash   
   was necessary.  Flashing    
   illuminated and extinguished the cord supervisory signal on the switchboard.    
   On some systems, it would route the call to an answering jack on the   
   switchboard.   
      
   --- SoupGate/W32 v1.03   
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