http://www.att.com/traveler/iacf/ccodes.html:
ATT documented country/city codes

http://arrow.cso.uiuc.edu/telecom/ld/pic-codes.html:
RLD carrier/PIC codes

http://www.555-1212.com:
Area codes and country codes

http://www.natltele.com/finder.html:
NPA/NXX locator

http://www.erlang.com:
Telecom traffic calculators by Westbay Engineers

http://www.htlt.com:
Telecom traffic calculator by Hillls

http://www.phonespell.org:
Phone number spelling calculator

http://www.phonetic.com:
Translates phone number to word and reverse; vanity number helper