In Bricker’s latest report, In the old days, why did phone numbers have names like “Circle 8745”? , he notes that, "The 555 (“KLondike”) exchange was never assigned to ordinary phone subscribers; dialing it connected you to the directory assistance operator, and it became a handy device for fictional phone numbers, as Cecil explains here . "
I see from Wikipedia that there have been further developments:
In fact, only 555-0100 through 555-0199 are now specifically reserved for fictional use, with the other numbers having been released for actual assignment. How, exactly, this will interact with the many uses of 555-2368 (long the “standard” fake number) by AT&T and other telephone companies, is no clearer than the reason for the choice of “2368”. …
In 1994, the North American Numbering Plan Administration began accepting applications for nationwide 555 numbers (outside the fictitious 555-01XX range). This would mean that a consumer from any area code could dial a seven-digit number such as 555-TACO, and the owners of that number could connect the call to the taco vendor nearest to the consumer. However, according to a 2003 New York Times article, the desired functionality requires the cooperation of local phone authorities, and most phone vendors have been reluctant to cooperate, perhaps wary of undermining the lucrative business of selling toll-free telephone numbers. Despite the fact that the service is virtually unavailable so far, most of the available 555 numbers have already been reserved.
The service Tellme uses the number 1-800-555-TELL (8355)…
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