Dial Tone Nostalgia

Luke and I were having an in-depth conversation about the UI for our Zeep Media product. We’re doing some really cool work with geographic targeting and report visualization on top of Google Maps. I’m sure that there will be subsequent blog posts about the technical challenges here.

I was trying to explain the NANP (North American Numbering Plan) and exactly what the NXX in NPA-NXX meant. NPA is a set of three numbers ([2-9][0-8][0-9]) that you will probably know as “Area Code” and NXX is just the next three digits.

So if we pick apart my number:

+1 (778) 227-3859

  • + means we’re using E164
  • 1 means we’re dialing in NANP
  • 778 is the NPA or area code
  • 227 is the NXX or exchange
  • 3859 is the station code

Unimportant as they may seem, the NXX digits used to prominently have a real, practical use.

Before cell phones, before digital-electronic switching, in fact before digital-mechanical switching there was the operator. The operator’s job was to manually connect wires running to people’s phones.



A telephone operator manually connecting calls with patch cables at a telephone switchboard.


As everyone knows, the best of systems can be ruined when you introduce human error, greed or incompetence. That brings us to an undertaker, Almon Brown Strowger. Almon was convinced that the local manual telephone exchange operators were sending calls to a competing undertaker business and thus set out to invent the automatic telephone exchange.

The exchange existed of a collection of Strowger Switches that would allow a phone connected to a wire pair on one side to dial using a set of pulses to connect a wire pair at the end, making another phone ring. Each switch would move the the corresponding index based on the number of pulses it received.

Dialing 3-8-5-9 a switch would take the first three pulses and place the initiating pair on the “3” circuit, the switch connected on that circuit there would then select the “8” circuit. As you can imagine, when you add a lot of numbers, say 10,000 of them, you need a lot of these switches. A lot of these switches would take up a lot of space. So, for every 10,000 numbers (0000-9999) there would be one building that housed all of these switches, the exchange. This is why old phones pulsed, they were actually moving a mechanical piece every time a pulse went over the wire.