The North American Numbering Plan, commonly known as the NANP, is the foundation of telephone numbering for the United States, Canada, and several neighboring territories. Understanding how the NANP works is essential for anyone building applications that validate, route, or send messages to phone numbers in the region. This article explains the structure of NANP numbers, why format alone is not enough to confirm deliverability, and how real-time validation fills the gap.
NANP Number Structure
Every NANP number contains 10 digits following this format:
(NPA) NXX-XXXX
- NPA — Numbering Plan Area (Area Code)
- NXX — Central Office Code
- XXXX — Subscriber Number
Example: (818) 555-1234
- 818 = Area code (Los Angeles)
- 555 = Exchange
- 1234 = Individual line
International use requires the +1 prefix (e.g., +1-818-555-1234).
Why the NANP Matters for Phone Validation
While numbers may appear valid structurally under the North American Numbering Plan, they do not necessarily function. Key concerns include:
- Area codes can be reused across different regions
- Some prefixes like 555 are reserved or non-routable
- Numbers get ported, deactivated, or reassigned
- Not all 10-digit numbers support SMS
A simple format check will confirm that a number matches the NANP pattern, but it cannot tell you whether the number is active, reachable, or capable of receiving a text message. That is where real-time validation becomes critical.
How CheckThatPhone Validates NANP Numbers
CheckThatPhone is purpose-built for U.S. and Canadian numbers within the NANP. The service uses real-time telecom data to verify:
- Active, routable status
- Line type classification (mobile, VoIP, landline)
- Portability and carrier details
- Deliverability and current condition
- Geographic and timezone information
You can review the full list of response fields in the API documentation.
Use Cases in B2B Messaging
- Sales lead qualification and filtering
- SMS campaign list cleaning
- Customer support call routing
- Fraud detection and prevention
- Signup form validation
Getting Started
The North American Numbering Plan provides a consistent structure for phone numbers, but structure alone does not guarantee that a number is valid or reachable. Real-time validation gives you the confidence to route, message, and score numbers accurately.
Read the CheckThatPhone documentation to see how NANP numbers are validated in practice, or explore available pricing plans to start validating numbers in your pipeline.