Number portability is the practice of allowing customers to transfer their telephone numbers from one operator to another.
Number portability became popular with the advent of mobile telephones, since in most countries different mobile operators are provided with different area codes and, without portability, changing one's operator would require changing one's number. Some operators, especially incumbent operators with large existing subscriber bases, have argued against portability on the grounds that providing this service incurs considerable overhead, while others argue that it prevents lock-in and allows them to compete fairly on price and service. Due to this conflict of interest, number portability is usually mandated for all operators by telecommunications regulatory authorities.
The world's first country to introduce number portability for mobile telephones was Singapore in 1997. In the United States, the FCC has mandated Wireless Local Number Portability starting November 24, 2003 (in metropolitan areas), and allowed operators to charge an additional monthly Long-Term Telephone Number Portability End-Use Charge as compensation. On November 10, 2003, the FCC additionally ruled that number portability applies to landline numbers moving to mobile telephones as well.
