you have AT&T to thank in 1947 and implemented in 1950/51. they are based on areas.

In the United States, phone numbers are fixed-length, with a total of 10 digits. The 3–3-4 scheme, developed by AT&T in 1947, uses three blocks of numbers arranged in two blocks of three and a single block of four digits. Look at the main phone number for HowStuffWorks as we go through the meaning of the different blocks.

Area code 919
Prefix 882
Line number 5000

http://www.howstuffworks.com/question659.htm

Nov. 10, 1951: Mayor M. Leslie Downing of Englewood, N.J., picked up a telephone and dialed 10 digits. Eighteen seconds later, he reached Mayor Frank Osborne in Alameda, Calif. The mayors made history as they chatted in the first customer-dialed long-distance call, one that introduced area codes.

Shortly after operators began using area codes, AT&T tested its new system, with help from the mayors. Englewood (area code 201) called Alameda (area code 415). The trial being a success, AT&T rolled out Direct Distance Dialing across America. Ninety area codes in 1951 grew to 135 in 1991.
http://www.corp.att.com/attlabs/reputation/timeline/51trans.html

The North American Numbering Plan (NANP) was developed by AT&T in 1947 and area code implementation began in 1950. Under that plan all telephone numbers in World Zone 1 (which covers the United States, Canada, Mexico and Caribbean countries) have the format: XXX-YYY-ZZZZ where:
http://5star-telemarketing.com/telephone-area-codes.html

Who is in charge of area codes?

Federal and state regulators share this responsibility. The North American Numbering Plan Administrator is responsible for day to day administration, assignment and management of area codes in the United States.

Congress gave the FCC jurisdiction over telephone number administration in 1996.

The FCC delegated to the states the authority to decide when, and in what form, to introduce new area codes.

Area codes may be added either by a geographic split or by an overlay. (See answer to the following question.)

The FCC receives advice on number administration issues from the North American Numbering Council (NANC), an advisory body made up of industry participants, consumer advocates, and state regulators.
http://www.fcc.gov/Bureaus/Common_Carrier/Factsheets/areacode.html

Developed in 1947 and first implemented in 1951 by AT&T, the NANP set out to simplify and facilitate direct dialing of long distance calls. Area code 201 was the first implemented under the plan.[1] It initially applied only to the U.S. and Canada, but at the request of the British Colonial Office, it was expanded to Bermuda and the British West Indies (including Trinidad and Tobago), due to their historic telecommunications administration through Canada as parts of the British Empire and their continued associations with that country, especially during the years of the telegraph and the All Red Line system.

http://en.wikipedia.org/wiki/North_American_Numbering_Plan

This is a list of North American telephone area codes in effect for the North American Numbering Plan (NANP). An area code is officially known as a Numbering Plan Area (NPA). An area code cannot start with a 0 or 1 because each digit represents either feature codes, operator assistance or the North American long distance prefix. Prior to 1995 all area codes had either 0 or 1 as the middle digit; all new codes from 1995 to present use 2 through 8.

http://en.wikipedia.org/wiki/List_of_NANP_area_codes