North American Numbering Plan (NANP) is a system used to organize and standardize telephone numbers across multiple regions and countries. Here are the key points:

1. Coverage: The NANP serves 25 regions across 20 countries, mainly in North America (such as the United States and Canada) and the Caribbean (such as Jamaica, Bahamas, and Trinidad and Tobago). This helps create a uniform system for dialing phone numbers across these regions, making international calls between them easier.
2. World Zone 1: Historically, these regions are part of a group called World Zone 1, which was established as part of a global division for phone numbering. Each world zone corresponds to a specific geographic region, and World Zone 1 was assigned to North America and parts of the Caribbean.
3. Country Code 1: All countries that participate in the NANP share the same country code, which is 1. This is why, when you make international calls to countries within this zone (like the U.S. or Canada), you start by dialing +1, followed by the area code (NPA) and the rest of the phone number.
4. Exclusions: Some countries in North America, like Mexico, do not participate in the NANP. Mexico has its own separate phone numbering system and uses the international country code +52. This means you need to dial a different country code when calling Mexico.