A phone number is a sequence of digits used to identify a telephone line for making or receiving calls and text messages. Although formats vary across countries and networks, most phone numbers follow a standardized structure defined by the International Telecommunication Union (ITU) under the E.164 numbering plan. Understanding the structure helps in international dialing, identifying regions, and developing telecom systems.
Basic Components of a Phone Number
Most phone numbers can be broken down into four main parts:
1. Country Code (CC)
The country code identifies the country or region of the phone number.
It usually consists of 1 to 3 digits.
For example:
United States and Canada: +1
United Kingdom: +44
India: +91
This code is used for international dialing and is recent mobile phone number data usually prefixed with a "+" sign or an international access code like "00".
2. National Destination Code (NDC) or Area Code
This identifies a specific geographic area, mobile network, or service within the country.
In landline systems, this is often referred to as the area code.
In mobile systems, it may represent the operator prefix.
For example:
New York (USA): 212
London (UK): 20
Airtel (India mobile): 981
3. Subscriber Number (SN)
The unique number assigned to the individual subscriber or customer.
This part identifies the exact phone line and is usually 6 to 8 digits long, depending on the country's number plan.
4. Trunk Prefix (Optional)
A trunk prefix is used for domestic dialing, usually when calling long-distance numbers within a country.
It’s not part of the international format and is typically removed when dialing from abroad.
For example:
In many countries, “0” is the trunk prefix (e.g., 020 in London becomes +44 20 for international use).
Example Structures
Let’s look at some examples:
Example 1: United States
International Format: +1 415 555 2671
Country Code: +1
Area Code: 415
Subscriber Number: 5552671
Example 2: United Kingdom
International Format: +44 20 7946 0958
Country Code: +44
Area Code (London): 20
Subscriber Number: 7946 0958
Trunk Prefix (for local calls): 0 (e.g., 020 7946 0958)
Example 3: India (Mobile)
International Format: +91 98102 12345
Country Code: +91
Mobile Prefix: 98102
Subscriber Number: 12345
Trunk Prefix: 0 (e.g., 098102 12345 locally)
Key Points
Phone numbers follow a logical, hierarchical structure: country → area/network → subscriber.
The E.164 standard allows up to 15 digits for an international phone number, excluding special characters.
Proper formatting ensures compatibility across telecom systems and avoids misdialing.
Conclusion
The structure of a phone number is designed to support both domestic and international communication. By understanding how each component works—from country codes to subscriber numbers—you can more effectively format, dial, and interpret phone numbers across different regions. This structure also supports the routing, billing, and management of global telecommunications networks.