I usehttp://www.areadecoder.com/for quick lookups, but the best ishttp://telcodata.us. It will give you a breakdown of each prefix, who
owns it, and in most cases the address (and a map) of the switch
location. Just go tohttp://telcodata.usand choose 'Area / Exchange'
under the 'Common Lookups' heading.
Thanks for the reference. Useful and interesting site.
Embedded in the internal exchange code for my city was two letters
that referred to the old original exchange name and rate zone for the
building which went back to manual or early dial days. Kind of neat
to see a legacy piece of technology continuing to this day. I wonder
if that applies to other big cities.
Also, I liked the cross-reference which showed other exchanges
operating out of the same building. Useful reference.