How are country codes assigned to phone numbers?

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Country codes for telephone numbers are assigned by the International Telecommunication Union (ITU), a specialized agency of the United Nations responsible for global telecommunication standards. Specifically, the ITU's Telecommunication Standardization Sector (ITU-T) manages the international numbering plan under Recommendation E.164.

The assignment process and underlying philosophy can be understood through several key points:

Global Zones: The world is initially divided into nine broad geographical zones or regions, and country codes typically begin with a digit corresponding to these zones. For instance:

Zone 1: North America (country code 1)
Zone 2: Africa (codes starting with 2)
Zones 3 and 4: Europe (codes starting with 3 or 4)
Zone 5: South and Central America (codes starting with 5)
Zone 6: Southeast Asia and Oceania (codes starting with 6)
Zone 7: Russia and surrounding regions (country code 7)
Zone 8: East Asia and some special services (codes starting with 8)
Zone 9: West, Central, and South Asia, and parts of Eastern Europe (codes starting with 9)
Application by National Authorities: When a country or a chinese thailand data sovereign entity (or an integrated numbering plan area, like the North American Numbering Plan) wishes to participate in the international public switched telephone network (PSTN), its national telecommunication administration applies to the ITU-T for a country code. This application is typically made by the recognized telecommunications regulator or ministry of that country.

Criteria for Assignment: The ITU-T considers various factors when assigning codes:

Uniqueness: The primary criterion is to ensure that each country code is unique globally to avoid any ambiguity in call routing.
Availability within Zones: Codes are assigned from the available pool within the respective geographical zones.
Efficiency: The ITU-T aims for efficient utilization of the numbering space.
Historical Context and Influence: The initial assignment of codes in the early to mid-20th century was influenced by the prevalence of rotary phones and the relative influence of countries in the ITU. Countries with more developed telecommunication infrastructures or larger populations sometimes received shorter (and thus "faster to dial" on rotary phones) codes. For example, the US and Canada share the single-digit code 1, and Russia uses 7.
No specific geographical boundaries for digits: While the first digit often corresponds to a geographical region, subsequent digits in a 2- or 3-digit country code are assigned based on availability and a systematic plan, not necessarily strict geographical proximity within that region. For instance, +31 is the Netherlands, +32 is Belgium, +33 is France, etc.
Length of Country Codes: Country codes can be one, two, or three digits long. Generally, larger or historically more influential countries often received shorter codes (e.g., 1, 7, 20, 30, 33, 44, 49), while smaller countries or those joining later often received longer codes (e.g., 389 for North Macedonia, 998 for Uzbekistan). This was partly to ensure that the total length of an international phone number (country code + national significant number) remained manageable for older switching systems, often capped around 11-12 digits in earlier plans, and now up to 15 digits under E.164.

The ITU-T maintains an official list of assigned country codes and continually updates it as new countries emerge, existing ones change their numbering plans, or specific codes are designated for non-geographic services like satellite phones (+881, +882) or international freephone services. This structured assignment process is fundamental to the global interoperability of telecommunication networks.