LNP - allows subscribers to keep their existing phone number when changing service providers, geographic locations, or service plans. It is often a mandated part of competitive deregulation. LNP is among the largest and most complex projects ever undertaken in the public switched telephone network (PSTN).

Local number portability was introduced to Local exchange carriers (LECS) in North America with the U.S. 1996 Telecommunications Act, which mandated compliance with Federal Communications Commision (FCC) recommendations governing the porting of subscriber numbers. In Europe, LNP has been driven by "directives" laid out by the Commission of the European Union.