1904 is not a country code. Numbers inside a country start like this: Callahan, FL (United States). The first digit 1 is the trunk prefix for domestic calls and is dropped from abroad.
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| Area or operator | From abroad | Inside the country |
|---|---|---|
 Callahan, FL · United States | +1 904 … | 1904 … |
| Fernandina Beach, FL · United States | +1 904 … | 1904 … |
| Florida · United States | +1 904 … | 1904 … |
| 11 more in United States | ||
| Area or operator | From abroad | Inside the country |
|---|---|---|
| Callahan, FL · United States | +1 904 … | 1904 … |
| Fernandina Beach, FL · United States | +1 904 … | 1904 … |
| Florida · United States | +1 904 … | 1904 … |
| 11 more in United States | ||
| Area or operator | From abroad | Inside the country |
|---|---|---|
 York · United Kingdom | +44 1904 … | 01904 … |
 Nirmand, Himachal Pradesh · India | +91 1904 … | 01904 … |
If a number starts with +, the first 1–3 digits are the country code. If it starts with 0 (8 in Russia and Kazakhstan), it is a domestic number: an area or operator code follows, and from abroad the 0 or 8 is replaced with + and the country code. The same digits can mean different places, so where the call came from matters.