Telecommunication services play an important role in our daily personal and business life, and therefore all activities in the telecommunication sector are received sensitively by everybody. Usually each national telecommunication market consists of one large (existing or former national) operator/service provider, with a well developed infrastructure and a large customer base, and of many small or medium sized privately held by alternative operators. 

Numbering is a limited resource. Moreover, mobile and fixed subscribers are emotionally and socially connected to their phone numbers. Bearing in mind that a telephone number (mobile or fixed) has become one of the most socially important pieces of information for a person or for business, changing your number when you migrate to new operator is very painful and doing so forms a large barrier for new alternative operators in their effort to attract new customers.

A number portability (NP) service enables telephone users to retain their telephone number when changing service providers. 
So the key purpose of number portability is to promote competition
and national regulation authorities play an important role in doing this. Usually the regulator sets the general requirements for number portability introduction after consultations with operators and services providers.

Benefits of number portability

Types of number portability 

Routing schemes for number portability

Keys to successful NP implementation