North American Numbering Plan Administration: Area Codes
Find North American codes by a map, number, or location. Includes information on future planned area codes and a free downloadable area code database.
http://www.nanpa.com/area_codes/index.html

International Dialing Codes
International and national direct dialing prefixes and instructions.
http://kropla.com/dialcode.htm

exUSSR Phone Codes
Includes all cities of Russia, Ukraine, Belorussia, Moldova, Lithuania, Latvia, Estonia, Kazakhstan, Georgia, Uzbekistan, Azerbaijan, Armenia, Kirgizia, and Tadjikistan.
http://phonecodes.narod.ru/

LincMad
Information about North American area codes, featuring changes, historical data and area code map. Detailed information on overlays and splits.
http://www.lincmad.com/

FAQs on Area Codes from FCC (USA)
The Federal Communications Commission answers frequently asked questions regarding area codes in the US.
http://www.fcc.gov/Bureaus/Common_Carrier/Factsheets/areacode.html

US Area Code Finder
Area code lookup for the United States with maps. Search by state or by code.
http://www.areacodesearchengine.com

UK Phone Information
Returns area information, map, BT charge information, and nearby exchange names for telephone numbers, access/short codes, or the name of a location.
http://www.ukphoneinfo.com/

US Switchboard - Area Code
Find United States area code by city and state, Find City and State by area code.
http://www.infospace.com/swbd.main/white-pages/reverse-lookup

Verizon - US Area Code Lookup
Find the major locations in a certain area code by entering the area code, or find the area codes that are used in a certain state by entering the state name.
http://www22.verizon.com/areacodes/

UK Dial Me
A directory of telephone STD dialing codes in the UK.
http://www.dialme.co.uk

World Search Dial Codes
Contains world telephone codes and time zone information. Search by city, country or number.
http://iptop.net/eng/code.html

NPA NXX Source
Databases for sale providing data on area codes and telephone exchange prefixes in the North American Numbering Plan.
http://www.npanxxsource.com

Dial Code
Find international dialing codes and area codes by specifying location. Information on direct dial prefixes. Flash user interface.
http://www.dial-code.com

Dial Codes Plus
Listing of international dialing codes and area codes with instructions.
http://dialcodesplus.com/

Time and Date
International dialing codes for almost any country and area codes for many cities. The interface includes a dropdown selector and local times are provided with dialing codes.
http://www.timeanddate.com/worldclock/dialing.html

World Telephone Numbering Guide
Lists and links to current international dialing codes and area codes with formatting guides and provides information on recent and historical changes.
http://www.wtng.info/

How to Call Abroad From US and Canada
Calling guide for United States and Canadian residents listing international country and city codes, phone books and time zones.
http://www.howtocallabroad.com/

Time Dial
Displays the current time, international dialing code, area codes and currency converter for almost anywhere. Includes instructions on country codes and international dialing code parts usage.
http://www.TimeDial.net

AT&T US Area Codes
List of US area codes for each state, with a list of important cities and towns in each of the telephone area codes. Provides good information on overlays and splits.
http://www.consumer.att.com/global/english/usa_codes.html

US Area Code Locations
Provides a list of towns and cities covered by each US area code including overlays and splits.
http://www.areacodelocations.info

US Area Code Answers
Information about US-based area codes and prefixes. Find the city, carrier, location, and more information about any phone number with this free service.
http://www.areacodeanswers.com

Assist Book
Lists international dialing codes, area codes, weather, world time and currency exchange rates. Also has a reverse phone number lookup tool.
http://www.assistbook.com

CountryCallingCodes.com
Online tool that builds dialing codes based on locations selected. Includes many international dialing codes and some area codes. Also has a reverse phone number lookup tool and current time.
http://www.countrycallingcodes.com

CountryCodes.com
Online tool that build dialing codes based on locations selected. Lists many international dialing codes and some area codes.
http://www.countrycodes.com

Fone Finder
Enter the 3-digit prefix or the city name to find an area code.
http://www.fonefinder.net

TP2Location
Resolve any telephone number to its geographical location.
http://www.TP2Location.com

US Area Codes, Rate Center, NPA, NXX etc Lookup
A free resource aimed at VOIP and telephone companies or individuals that need to gather information about US phone numbers or to determine information such as which phone numbers would be local to a particular location. The data is availible as XML for computer programs to read.
http://www.localcallingguide.com/