US Phone Number Format — Area Codes, Formatting & Examples

US phone numbers follow the North American Numbering Plan (NANP), a system shared with Canada and several Caribbean nations. Every US number consists of a country code (+1), a three-digit area code, and a seven-digit local number. This guide covers the complete format, area code system, formatting conventions, toll-free numbers, and how to dial the US from abroad.

US Phone Number Structure

A complete US phone number has 10 digits (or 11 with the country code):

The three components are:

The local number is further divided into a 3-digit exchange code (also called the central office code) and a 4-digit line number. In the example above, 555 is the exchange and 0198 is the line number.

How Area Codes Work

Area codes (officially called Numbering Plan Areas, or NPAs) were introduced in 1947 to enable direct long-distance dialing. The original system assigned area codes based on population — cities with more phone traffic received codes that were faster to dial on rotary phones (lower digits first, like 212 for New York City).

Key rules for area codes:

• The first digit is always 2-9 (never 0 or 1)
• Area codes like N11 (211, 311, 411, 511, 611, 711, 811, 911) are reserved for special services
• Originally, the middle digit was 0 or 1 — this restriction was lifted in 1995 as more codes were needed
• A single state can have many area codes (California has over 35, Texas has over 25)
• Area code overlays mean multiple codes can serve the same geographic area

Formatting Standards

There are several accepted ways to write a US phone number. All are correct, but conventions vary by context:

Toll-Free Numbers

Toll-free numbers allow callers to reach a business without being charged for the call. The business pays for incoming calls instead. Toll-free area codes are:

All toll-free numbers follow the same 10-digit format as regular numbers: 1-800-XXX-XXXX. Vanity numbers spell words using the phone keypad (e.g., 1-800-FLOWERS = 1-800-356-9377).

Dialing the US from Abroad

On any mobile phone worldwide, you can use the + prefix (usually by long-pressing the 0 key) followed by 1 and the 10-digit number. This works from every country.

Common Area Codes by State

Mobile vs. Landline Numbers

Unlike many other countries (UK, Australia, Germany), the United States does not distinguish between mobile and landline numbers in the numbering format. Both types share the same area codes and follow the same 10-digit format.

This means:

• You cannot tell from a US phone number whether it is a mobile or landline
• Area codes are shared between mobile and landline numbers
• Number portability allows users to move their number between mobile carriers and even between landline and mobile services
• VoIP services (Google Voice, Vonage, Ooma) also use standard area codes

For SMS delivery, this distinction matters — if you need to know whether a US number is mobile-capable, you must use a phone number lookup service (like Twilio Lookup or NumVerify).

Reserved Telephone Numbers

Certain US phone numbers are reserved and will never be assigned to real subscribers:

• 555-0100 to 555-0199 — reserved for fiction (movies, TV, books) in every area code
• 555-1212 — directory assistance
• 911 — emergency services
• 411 — directory information
• 311 — non-emergency government services
• 211 — community services and information
• 511 — traffic and transportation information
• 711 — Telecommunications Relay Service (TRS) for hearing/speech impaired
• 811 — call-before-you-dig utility locating

Frequently Asked Questions