Certain numbers are immutable. The eight-ball will never spill into the pocket only to re-emerge in the trough as a 32-ball; party-goers, no matter how nattily garbed, may only aspire to be dressed to the nines, not to the 67s; nor will tactless beans-spillers ever have cause to reflect, "In for a penny, in for pounds 3." And so it has been that bottom-line-loving Manhattanites, accustomed to believing in the constancy of numbers, if of little else, have felt safe in supposing that their signature telephone code, 212, would remain long after California slipped into the Pacific. The Rockies may crumble, the logic went, but the Big Apple's core was here to stay.

When London succumbed to its number shift a few years ago, not one New Yorker shuddered. "Could never happen here," they assured themselves as technicians needlepointed new phone hook-ups into the thatch of each resident's obligatory fax machine, beeper and second phone line. "Tough luck," they sympathised, ordering cell-phones and cordlesses and opening phone-glutted home offices and kitsch cafes. Their supply of numbers, they knew, was numberless.

And then, suddenly, infinity ran out; a number crunch hit Manhattan. By next June, the papers ominously blare this month, the phone cabal expects to start weaving in a new exchange, costing a fortune in new letterhead and an inestimable price in native self esteem. To intensify the blow, the new number chosen is 646 - one digit shy, superstitious citizens noted, of the Sign of the Beast - and worse still, only some New Yorkers would have to submit to it, while others would be left unscathed.

As a result, a historic battle is now building which threatens to pit brother against brother, mother against child, uptown against downtown. One going scheme is to divide Manhattan into two zones; one a graced zone that gets to hold on to the life-giving 212, which will lie above 23rd Street; another an outcast wilderness including SoHo, Tribeca, Wall Street, and the Village, which will have to swallow the shame of 646. Another scheme would allow established 212ers to hold on to their numbers, but allot 646 to all future phone lines, something critics have described as a "screw-the-newcomers plan." Brooklyn and Queens, already subjected to the less zippy 718, will be forced to accept an additional code, too - 347. "What kind of area codes are these?" city commentators roared. "Area codes so forlorn, they are held together by an apologetic 4!"

Until the numbers ran out, prestige numbers in the States always had appealing mnemonic, quick-dialling codes Los Angeles exulted in 213, Washington revelled in 202, Chicago gloated over its 312. As a special mark of favour, Los Angeles received a second posh prefix, 310, when the 213s were not enough. New York, it goes without saying, has not fared as well, especially considering that even if 646 is added, an additional code will need to be tacked on at the dawn of the next millennium.

Emotions are running high; enraged citizens have been given a phone number to call to register their complaints, while city brahmins pester their lawyers to pencil phone-number-preservation clauses into their wills. Meanwhile, at public hearings, downtowners and uptowners hurl recriminations at each other, each explaining why his part of town deserves to keep 212. Before the confrontation has ended, the rivalry of the Guelphs and Ghibellines, of Abel and Cain, of Hatfields and McCoys will seem mere contretemps.

The solution to the problem - adding an eighth digit to American phone numbers, and so making the invention of unwieldy new prefixes unnecessary for the next few centuries - has been rejected out of hand, as it does not contribute sufficiently to civic paranoia.