An American phone number might look like (999) 555-2324, grouped by area code, prefix and intralata numbers in standardized groups using standard punctuation. When I was a kid in the 70s, local numbers might have their entire prefix reduced to a location, like RO4 instead of 764 with the RO standing for ROckville Centre. In the UK phone numbers can be grouped differently and in some countries they can seem very long.
What's the history of the phone number? How did these groupings become agreed upon? Who decided on local prefix codes like RO4? What determines their length? How long was the first phone number and who had it? Were there any phone number controversies?
The first groups of telephone subscribers told a central-office operator to whom they’d like to be connected, and that’s the system you see in old Andy Griffith shows, when Sheriff Taylor just picks up the receiver and says “Sara, get me Aunt Bee.” In 1879, fears that a Lowell, Mass., measles epidemic would require unskilled substitutes to step in, a local physician recommended that subscribers begin asking for parties by number. That improved efficiency enough that the idea spread quickly.
At the time, an exchange was an actual building, where up to 1000 subscriber lines came together and could be connected by operators, one line to another. A Kansas City undertaker named Albert Strowger in 1889 became convinced that operators were directing dead-body business to other undertakers, and invented the step-by-step switch that allowed subscribers to dial their own numbers—at least within the same exchange. So if you knew that Gower’s Pharmacy was phone number 404, you could dial it yourself. (Some cities had competing phone companies at the time, so Gower’s ads in the local newspaper might give the phone number as “Phone 601 or Automatic 404.”) Now you only had to ask an operator to place your call if you needed to be connected to an exchange in a nearby town, or in another part of a big city, and you did so by asking for a connection to “Mayberry 322” or “Harrison 7186.” Most of these exchange names in big cities were geographically meaningful, so long as they could easily be distinguished when heard.
When subscriber dialing was introduced in the 1920s in large cities, the users dialed the first three letters of the exchange name using the letters on the phone dial, followed by the four numbers for the specific line to ring. So the three-digit numbers represented by the names now had to be distinctive. That still left some room for creativity, but new exchanges in growing areas often needed to use letters that didn't suggest anything very local. When Chicago North Shore suburbs were given 257, for example, that doesn't spell much except ALPine.
In the late 1940s, big cities shifted to "2 + 5" dialing, a Bell System standard. To make the conversion easy, the third digit was kept the same wherever possible. So if your number had previously been HARrison 7186, now it was HA7-7186, since the R dials 7 anyway. In some places this seamless transition wasn't possible—but more importantly, new third digits could be introduced to expand capacity.
Eventually that system also reached its limits: you can't spell anything for a number beginning with 95 or a few other combinations. All-number dialing was the standard for new phone numbers by the 1970s, but since the phone book publishers only re-typeset entries that needed to be changed, many big-city phone books still listed old-style numbers until the early 1980s.
Meanwhile, the Bell System was moving toward subscriber dialing of even long-distance calls, and in the 1940s developed the North American Numbering Plan that assigned area codes to geographic regions, within which prefixes had to be unique three-digit groups (though subscribers might still know them as BUtterfield 8 or whatever). North America had been designated with the international calling code 1, so now all elements were in place for the White House to be reachable from anywhere in the world at 1 (202) 456-1212.
So far, I’ve talked about North America exclusively. As best as I can tell, telephone operators in other parts of the world for most of the 20th century mostly followed a few years behind the advances made and implemented by the Bell System. But as numbers of subscribers, and later number of phone lines (due to mobiles) grew rapidly, other countries faced the problem of insufficient numbers, and many went to eight-digit local numbers, then added additional “area codes” as geographic overlays or to serve mobile phones. Of course, local practices regarding how numbers are written differ, so the Bell System recommended parentheses around area codes and a hyphen between prefix and line number. Meanwhile the French famously wrote phone numbers in pairs—42 27 71 86—while some places put the new eight-digit numbers in two equal groups and others in uneven groups the way we’re used to prefix-and-number.