You can automatically add a local area code to phone numbers you dial. This setting is found in the Phones section of your account under Device Settings:
A click on the ON/OFF slider button enables or disables the automatic area code setting.
The default setting is 00, which allows the dialling of international phone numbers without a leading 00 or +.
If you set this to an area code like 020, any phone number that doesn't start with a 0 will be dialled with the chosen area code. This allows dialling a local subscriber number directly without using an area code, which is a well-known telephony feature of legacy telephony systems.