0331 is not a country code. Numbers inside a country start like this: Potsdam (Germany), Feni/Sonagazi/Chagalnaiya/Daganbhuyan (Bangladesh), Jember (Indonesia), Ufone (Pakistan) 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 |
|---|---|---|
 Potsdam · Germany | +49 331 … | 0331 … |
 Feni/Sonagazi/Chagalnaiya/Daganbhuyan · Bangladesh | +880 331 … | 0331 … |
 Jember · Indonesia | +62 331 … | 0331 … |
 Ufone · Pakistan | +92 331 … | 0331 … |
 Botoșani · Romania | +40 331 … | 0331 … |
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.