In order to accommodate inbound DDD, it was essential that every
> number have a 7-digit format. But SxS switches couldn't accommodate
> 7-digit dialing, so telcos faked 7-digit numbers by prepending dummy
> digits. Local calls continued to be dialable with only four or
> fivedigits; however, if a local caller actually dialed all seven
> digits, the prepended digits were absorbed by "absorbing selectors" -- > i.e. ignored.
I don't understand. Below is the local dialing plan we had when I was in school. Carbondale, IL, (Jackson County) 1971 General Telephone
618-453 - So. Il. Univ., Carbondale. IL 618-457 - Carbondale, IL 618-549 - Carbondale, IL 618-867 - De Soto, IL 618-684 - Murphysboro, IL 618-687 - Murphysboro, IL From/to any Carbondale NXX (1, 2, or 3): 5-digits allowed, 7-digits supported (618-453 required a ?9? to dial out from the university, but 5-digits allowed within the university PBX/Centrex/whatever) From Carbondale NXX (1, 2, 3) to De Soto (4): 7-digits required From Carbondale NXX (1, 2, 3) to Murphysboro, (5, 6): 7-digits required. From Murphysboro or De Soto to Carbondale, 7-digits required. (I believe that locally, only 5-digits were required in Murphysboro and only 4-digits in De Soto.) Outside of these 3 exchanges, but within the 618 NPA: 1+7-digits required Outside the 618 NPA: 1+NPA+7-digits required Carbondale had DDD in the 60's. It did use '150' instead of just '1' as a toll alert and the operator would come on the line and ask 'Your Number Please?'