The prefix 1 is used as part of the international dialing code +1, which is the country code for the North American Numbering Plan (NANP). This means it covers the United States, Canada, and several Caribbean nations and territories that share NANP numbering, not just the U.S. alone.
- Primary country(s): United States and Canada.
- Other NANP members that use +1 alongside the U.S., typically identified by the subsequent three-digit area codes: several Caribbean nations and territories such as Bahamas, Barbados, Barbados, Anguilla, Antigua and Barbuda, and others.
- How to tell origin: after +1, look at the three-digit area code that follows to determine the specific country or region within NANP.
Notes for context:
- Many sources emphasize that +1 is shared under the NANP umbrella, which is why the same prefix (+1) is used for both the U.S. and Canada, as well as multiple Caribbean destinations.
- When interpreting a call or number starting with +1, the exact country can often be inferred from the next few digits (the area code), which maps to a particular region or country within NANP.
If you need, I can provide a concise list of all NANP countries and territories that use +1 with their corresponding area code ranges.