01 is not a country code. Numbers inside a country start like this: Vienna (Austria), Zagreb (Croatia), EriTel (Eritrea), Dublin (Ireland) 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 |
|---|---|---|
 Vienna · Austria | +43 1 … | 01 … |
 Zagreb · Croatia | +385 1 … | 01 … |
 EriTel · Eritrea | +291 1 … | 01 … |
 Dublin · Ireland | +353 1 … | 01 … |
 Bahan · Myanmar (Burma) | +95 1 … | 01 … |
| Bayintnaung · Myanmar (Burma) | +95 1 … | 01 … |
| Yangon · Myanmar (Burma) | +95 1 … | 01 … |
 Lima/Callao · Peru | +51 1 … | 01 … |
 Ljubljana · Slovenia | +386 1 … | 01 … |
 Mogadishu · Somalia | +252 1 … | 01 … |
 Sanaa · Yemen | +967 1 … | 01 … |
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.