So what exactly is Local Number Portability?

Defined by the 1996 Telecomminications Act:

"The ability for users of telecommunications services to retain, at the same location, existing telecommunications numbers without impairment of quality, reliability, or convenience when switching from one telecommunications carrier to another."

Local Number Portability is a Service Provider Portability rather than a Location Portability. LNP enables end-users to keep the same telephone number when subscribing to a new telephone service provider.

Defined by the North American Numbering Council:

NANC, which recommends industry standards to the FCC, took this definition one step further:

LNP also allows end-users to move (or relocate) within a designated Rate Center and retain their telephone number, which was previously limited to moves within a Switch or Serving Wire Center (SWC). A Rate Center is a geographic location defined by Vertical and Horizontal (V&H) coordinates. These coordinates are used to determine the airline mileage that, in turn, is used to determine charges. One Rate Center may contain serveral Wire Centers.

Currently, the "area of portability" is confined to these designated Rate Centers. Portability outside or between Rate Center boundaries is not allowed, but may come later as the industry migrates to "Location Portability" (also referred to as "Geographic Portability")