United States Phone Numbers: Format, Area Code & Validation Guide - phone-number-standards -

Frequently Asked Questions

Missouri phone numbers follow the North American Numbering Plan (NANP) format: +1 (NXX) NXX-XXXX, where N is any digit from 2-9, and X is any digit from 0-9. 10-digit dialing is mandatory for local calls (area code + 7-digit number), while long-distance calls require a "1" prefix before the area code.
The North American Numbering Plan (NANP) format is +1 (NXX) NXX-XXXX. "+1" is the country code, N represents digits 2-9, and X represents digits 0-9. This structure is used for US and Canadian phone numbers and is essential for call routing and validation.
Missouri requires 10-digit dialing due to the implementation of area code overlays. Overlays assign multiple area codes to the same geographic region, necessitating 10 digits to route calls correctly. This ensures calls reach the intended recipient even with overlapping area codes.
As of 2025, 10-digit dialing is mandatory for all local calls within Missouri. You do not need to dial "1" before the area code for local calls. While there may have been grace periods previously, ensure consistent 10-digit dialing for all local calls going forward.
No, 7-digit dialing is no longer supported in Missouri as of 2025. The transition to mandatory 10-digit dialing ensures accurate call routing with area code overlays. You must use the area code + 7-digit number for all local calls in Missouri.
The exchange code is the three digits immediately following the area code (NXX) in a North American phone number. The first digit (N) must be 2-9, while the second and third digits (X) can be 0-9, excluding N11 patterns like 911.
Ensure the first digit is 2-9 and avoid reserved N11 codes (like 211, 411, 911). The provided JavaScript example demonstrates how to build this validation logic, checking the first digit and excluding specific patterns.
E911 compliance mandates features for accurate emergency response. This includes direct 911 dialing (no prefixes), automatic location transmission to PSAPs, and notification of designated personnel with location information when 911 is dialed, as required by Kari's Law and RAY BAUM's Act.
Use multiple location methods like GPS, Wi-Fi, and cellular triangulation with fallbacks for accurate location data. Implement a system to format dispatchable location information according to PSAP requirements, including street address, floor level, and room number, as required by RAY BAUM's Act.
Carrier integration requires redundant location services, number portability support via NPAC queries and LRN routing, and rigorous testing. Different port types have varying completion times, ranging from 1 business day for simple wireless ports to 5+ days for complex ports.
Number portability allows users to keep their number when changing providers. Your systems must handle this by querying the Number Portability Administration Center (NPAC) to determine the correct carrier and using Location Routing Numbers (LRNs) for accurate routing. Somos, Inc. currently administers the NANP, including number portability.
Porting timelines vary: simple wireless ports take 1 business day, wireline-to-wireless takes 4, and complex ports 5+ days. These timelines impact user experience and should be managed carefully. Be prepared for potential delays.
Dial "1" + area code + 7-digit number for domestic long-distance calls from Missouri. For international calls, use 011 + country code + number. Local calls require 10-digit dialing without a "1" prefix.
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