1678 is not a country code. Numbers inside a country start like this: Acworth, GA (United States). The first digit 1 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 |
|---|---|---|
 Acworth, GA · United States | +1 678 … | 1678 … |
| Alpharetta, GA · United States | +1 678 … | 1678 … |
| Atlanta, GA · United States | +1 678 … | 1678 … |
| 28 more in United States | ||
| Area or operator | From abroad | Inside the country |
|---|---|---|
| Acworth, GA · United States | +1 678 … | 1678 … |
| Alpharetta, GA · United States | +1 678 … | 1678 … |
| Atlanta, GA · United States | +1 678 … | 1678 … |
| 28 more in United States | ||
| Area or operator | From abroad | Inside the country |
|---|---|---|
 Bala · United Kingdom | +44 1678 … | 01678 … |
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.