066 is not a country code. Numbers inside a country start like this: Vodafone (Ukraine), DTAC (Thailand), Telekom Srbija a.d. (Serbia), Água Boa - MT (Brazil). 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 |
|---|---|---|
 Vodafone · Ukraine | +380 66 … | 066 … |
 DTAC · Thailand | +66 66 … | 066 … |
 Telekom Srbija a.d. · Serbia | +381 66 … | 066 … |
 Água Boa - MT · Brazil | +55 66 … | 066 … |
| Alta Floresta - MT · Brazil | +55 66 … | 066 … |
| Alto Araguaia - MT · Brazil | +55 66 … | 066 … |
| 74 more in Brazil | ||
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.