North American telephone numbers with a prefix of 555 (NPA-555-XXXX) are put in a special class, "555 line numbers," by the North American Numbering Plan. According to NANPA, "555 numbers are used to reach a wide variety of information services." They are assigned for either local (single area code) or national use.
A complete listing of assigned 555 line numbers is too long and changes too often to publish here; it may be downloaded from the NANPA Web site (http://www.nanpa.com/number_resource_info/555_numbers.html).
However, it is interesting to note that line numbers 100 through 199 are allocated as "RESERVED FICTITIOUS USE"—thus you may presumably use any 555-01XX phone number in a work of fiction without fear of legal liability.
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