Number Portability

Number portability is the ability of users of telecommunications services in the United States and most other countries to keep their existing telephone number when changing from one local service provider to another. Under Federal Communications Commission (FCC) rules, the implementation of local number portability (LNP) in the United States has caused some problems for telephone survey researchers. In the early days of wireline-to-wireline portability, both numbers associated with a porting request could be dialed successfully. When wireline-to-wireless porting was implemented, there were concerns that this would influence the ability of researchers and telemarketers to comply with the portion of the Telephone Consumer Protection Act (TCPA) of 1991 that limited calls to certain types of phone numbers, including wireless phone numbers.

In 1996, the U.S. Congress amended the Telecommunications Act of 1934 to establish a framework that would promote competition and reduce regulation in all telecommunications areas. It was recognized that certain barriers to competition would need to be eliminated, specifically the inability of customers to switch from one service provider to another and retain the same phone number. New FCC rules were enacted that gave consumers the ability to switch from one service provider to another and keep their existing telephone numbers. The rules were applicable only locally, that is, only within a local exchange or rate center. If a person moved from one geographic area to another, the number would not be portable. Telephone companies were allowed to charge a fee to cover their porting costs. However, because of these costs, most small landline companies were not required to port numbers to wireless carriers until the FCC had completed a study about the effects of porting rules on small companies.

Local number portability in the United States was implemented in phases. Portability between local land-line (wire) service providers was implemented in 1998. The FCC had also required that three categories of CMRS (commercial mobile radio service) providers—cellular providers, broadband personal communications service (PCS) providers, and covered specialized mobile radio (SMR) providers—also provide number portability. The commission concluded that requiring them to do so would promote competition between and among local landline and wireless services. A separate timetable for compliance was established for CMRS providers. LNP between wireless service providers was finally implemented in November 2003 and between landline and wireless services in early 2005.

Porting in the United States requires two 10-digit numbers. One is the original subscriber number, which is no longer a valid local routing number or switch, and the other is a number in a prefix or 1000-block belonging to the new carrier that is used for rerouting a call to the correct end-user location and for accounting. A 1000-block is a block of 1,000 consecutive local numbers within a prefix, all starting with the same seven digits (e.g. 203-255-1XXX). Within a prefix, 1000-blocks can belong to different service providers offering different types of service. Since the subscriber's new carrier can also provide telephone service to new or existing customers as well as customers that are changing carriers, these remote porting numbers can and do occur in 100-blocks found on list-assisted RDD databases. A 100-block is a block of 100 consecutive numbers starting with the same eight digits (203-333-65XX). List-assisted RDD frames normally contain only 100-blocks with one or more directory-listed numbers from which RDD samples are generated by appending a random number between 00 and 99 to selected 100-blocks. Once a new subscriber (e.g. 203-333-6555) appears in a telephone directory, the 100-block 203-333-65XX becomes eligible for RDD samples. During the generation of an RDD sample, both kinds of numbers—those belonging to regular subscribers and those belonging to subscribers that have ported their number to this new carrier—can be generated during random number assignment.

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