In the United States it replaced the practice of allocating all 10,000 numbers of a central office prefix at a time.
Telephone number pooling was first tested for area code 847 in Illinois in June 1998, and became national policy in a series of Federal Communications Commission (FCC) orders from 2000 to 2003.
The landline telephone systems evolved over a period of over one hundred years before diversification, so that it was technically difficult to share infrastructure between multiple providers.
Central offices were established based on local demand and convention, and dialing prefixes were assigned to single providers who managed the plant in each location.
Additional mobile carriers entered the market to provide digital service (such as GSM, introduced in 1991).
In 1985, competitive access providers (CAPs) began to offer private line and special access services; originally based on private branch exchange (PBX) standards such as direct inward dial, these evolved into competitive local exchange carriers (CLEC).
Every broadband Internet provider could become a telephone company, with telephony merely being one more application running over the packet-switched network.
There was no requirement that the Internet to telephony gateway be operated by a facilities-based telco or cable company; anyone could buy a large block of telephone numbers from a CLEC, deploy a server to feed the calls to broadband Internet and offer telephone service.
[10] The state's telecommunications regulator, the Illinois Commerce Commission, at the urging of consumer advocates,[11] pushed back against industry and FCC demands for a distributed overlay for 847 from 1999 to 2001[12] as half of the existing 847-numbers were not in use.
[14] A similar fight by New York state's Public Service Commission to maintain seven-digit dialing within the same area code (including calls within 212) was also unsuccessful.
[15][16] An attempt by the United States Telecom Association, a trade group of local telephone companies, to propose mandatory ten-digit dialing nationwide was rejected by the FCC in 2000.
[33] Local exchange routing databases now include a "block ID" to indicate the ownership of the specific sub-blocks within a prefix.
An example of a small hamlet with number pooling is La Fargeville, New York (population 600), in the 315/680 area codes.