0904 is not a country code. Numbers inside a country start like this: NCell (Nepal), Airtel (Nigeria), T-Mobile (Slovak Telekom) (Slovakia), Syriatel (Syria) and others. The first digit 0 is the trunk prefix for domestic calls and is dropped from abroad.
Have the full number? Check it in the number lookup.
| Area or operator | From abroad | Inside the country |
|---|---|---|
 NCell · Nepal | +977 904 … | 0904 … |
 Airtel · Nigeria | +234 904 … | 0904 … |
 T-Mobile (Slovak Telekom) · Slovakia | +421 904 … | 0904 … |
 Syriatel · Syria | +963 904 … | 0904 … |
 Taiwan Mobile · Taiwan | +886 904 … | 0904 … |
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.