Do I include the leading ‘1’ in a phone number?

A leading ‘1’ in a phone number is called a ‘trunk prefix’ – it is used to notify the circuits of the telephone network to route the call to a different region of the phone network.

The North American Numbering Plan (NANP) uses it. Mongolian phone numbers use a leading ’01’ or ’02’ that functions as a trunk prefix, however, this page does not include the Mongolian phone system.

It is similar to a leading ‘0’ used in Europe, Asia, Australia, and New Zealand, as well as some countries of South America and Africa.

On this page

Where to find a leading ‘1’

A leading ‘1’ is found in countries using the NANP – Canada, the United States, a majority of Caribbean countries & regions, as well as U.S. territories in the Pacific.

The Mexican phone system uses a leading ‘1’ for mobile phone numbers. When calling from another country, add it into the call sequence after the country code and before the local number.

The Mongolian phone system uses a leading ’01’ or ’02’ as a trunk prefix.

Dialing within the same NANP country/region

… long distance

When making a long distance call, the leading ‘1’ is included in the call sequence.

In many regions, phone networks have been upgraded so that if a call is placed without the leading ‘1’, the call will still be completed after a message informing the caller that the call will be charged at long distance rates.

… locally

When making a local phone call, the leading ‘1’ is dropped from the call sequence.

Dialing from outside an NANP country/region

… from another NANP country/region

When calling to an NANP country/region from another NANP country/region, the leading ‘1’ is included in the call sequence, however, there is no ‘011’ that is common for placing an international call to a region outside of the NANP.

Example: The Metropolitan Museum of Modern Art in New York City, United States lists its phone numbers as (1) 212-535-7710.

The call sequence would be the same if the person calling the museum was located in Los Angeles, USA, Montreal, Canada, or Kingston, Jamaica.

… from a region outside the NANP

When calling from outside the NANP, the leading ‘1’ is included however acts as the country code.

The next 3 digits (the first 3 digits of the 10 digit number) act as the area code that determine which country / region the call is routed to.

Mexican mobile phones

Mexican mobile phone numbers have a ‘1’ added to the call sequence when calling from outside Mexico.

When calling, place a ‘1’ between the Mexican country code (+52) and the mobile phone number that is being dialed.

Mongolian trunk prefix

Mongolia uses ’01’ or ’02’ as a trunk prefix.