On Wednesday, June 25, 2014 5:00:35 PM UTC-4, Adam H. Kerman wrote:   
   > In the example I gave, Cook County is huge and includes the entire city of   
   Chicago plus a substantial portion of the suburban area. A county has   
   facilities all over the place.    
      
   Philadelphia isn't as large as Chicago and certainly smaller than Cook   
   County.  But the old Phila Centrex/PBX did serve most city* offices and   
   facilities throughout the city, which covered a reasonably large area.  Calls   
   could be transferred to different    
   locations by the City Hall operator.  The City Hall switchboard was a 24   
   position 608.  Operators plugged into a trunk group and dialed the last two or   
   three digits of an extension; a method used on large systems.  I think it was   
   served by a No. 5    
   crossbar.   
      
   The system was a hybrid of Centrex and PBX.  There were many extensions that   
   could not be dialed from the outside.  The system retained its old system for   
   years--offices had plain rotary phones long after the rest of the world went   
   Touch Tone--but it has    
   been since upgraded.  The DID got another prefix so all extensions can now be   
   dialed from the outside.   
      
   *The Phila city and county cover the same area, and coun