Where can I find a list that correlates area codes to cities / counties?

I've found area code lists that relate area codes to states, but was curious how NANPA was providing the area code to city located here: a href="http://www.nanpa.com/nas/public/npa_city_query_step1.do?method=resetNpaCityReportModel" rel="nofollow"http://www.nanpa.com/nas/public/npa_city…/a