The short answer
Start with international format and match the longest relevant assigned calling code. Do not infer a person’s nationality or physical location.
Look for a leading plus
A plus sign marks international-format input; without it, the same digits can be ambiguous across national plans.
Read the full plan
The +1 plan covers multiple countries and territories, while +7 is shared by Russia and Kazakhstan. A code is not always one country.
Continue only as far as supported
Use the national plan for range and type. A mobile subscriber may live or travel outside the code’s country.
A country code is not always one country
Start with the international + prefix. Then distinguish the calling code from the national digits that follow.
| Prefix | Safe interpretation | Unsafe shortcut |
|---|---|---|
| +44 | UK numbering plan | The person is currently in the UK |
| +1 | Shared North American numbering plan | Every +1 number is in the United States |
| +7 | Shared Russia / Kazakhstan code | Every +7 number belongs to Russia |
When a code is shared, stop at the shared plan until a more specific allocation supports the next conclusion.