Foreign exchange service (telecommunications)
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In telecommunication, a foreign exchange service (FX) is a network-provided service in which a telephone in a given local area is connected, via a private line, to a central office in another, i.e., "foreign", exchange, rather than the local exchange area's central office.
To call originators, it appears that the called party having the FX service is located in the foreign exchange area.
[edit] Purpose
In basic telephony there are two types of offices: local and foreign. A local office was assigned a specific area, and all telephone services provided to that area came from that central office. Each central office had its unique identifier. In the early days names were used, such as "Jackson" or "Newton" or the like. The office names became NNX codes which are the three-digit prefixes for your telephone number (not the area code).
Customers who want a telephone number provided by a neighboring telephone central office, lease a "foreign exchange" line. With the old two-wire loop technology, this would require an engineered circuit with increased costs. The practice is rare except in big cities.
