ITU-T Recommendation E.164 is a global PSTN and data network which arranges telephone numbers to help with call routing. This global framework allows any country to create international phone numbers of up to 15 digits (excluding the international call prefix). 

Today, the United Nations handles information and telecommunication technology (ICT) issues through its International Telecommunication Union (ITU). This agency governs the ITU-T, or Telecommunication Standardization Sector, which itself developed E.164 and its related recommendations. 

Another player is the World Telecommunication Standardization Assembly (WTSA), which meets every four years to address the most pressing telecommunication problems. E.164 is a set of recommendations the ITU has implemented over several years. 

Why should you care about E.164? 

E.164 serves as a successor to E.163. In 1997, it was clear a new numbering method was necessary to accommodate the new age of ISDN. 

Compared to the previous framework, E.164 improves dialing, especially for larger companies with offices around the world or anybody who travels cross-border often.  

Among the changes is raising the maximum number of digits a telephone number can have from 12 to 15, enabling future growth to support more users. 

E.164 is also backward compatible with legacy technologies. Even rotary dial phones can work with the new numbers. 

E.164 compliant phone numbers must include the following three fields: 

• The country code (one to three digits long) 

• The national destination code (NDC), which indicates the specific jurisdiction in the country where the caller is. You might know of it as an area code or international city code. 

• The subscriber number (SN) 

The NDC and SN together make up the national number. Countries have the freedom to decide on the length of the national number if it’s no longer than E.164’s 15-digit limit. 

For international public communications, E.164 also dictates the numbering structure for various categories of users, including: 

• Geographic areas: Particularly countries with their own integrated numbering plans. These numbers have a country code between one to three digits followed by a national number up to 15 digits. 
• Global services: Have a three-digit country code, a one to four-digit identification code (IC), and a subscriber number no longer than 11 digits. 
• Networks: Those which do not start with international prefixes, have a three-digit country code, a one to four-digit identification code, and a subscriber number with a maximum length of 12 digits. 
• Groups of countries: Have their own numbers too. A three-digit country code is first, followed by a single-digit group ID code and a subscriber number with a maximum length of 11. These numbers do not contain a national prefix. 
• Trials: Have their numbers always beginning with 991. The second field is a single-digit trial ID code, and the last portion is a subscriber number of at most 11 digits. 

How does Sinch work with E.164? 

Maintaining compliance with international calling standards is no easy task on your own. Partner with Sinch and leave the complex calling standards to us. 

We offer a wide range of internationally-compliant voice solutions, including numbers, number porting, toll-free numbers, and more to support your international calling needs.