These settings are only required for countries in North America.
A dialing code rule defines a series of phone numbers which must be dialed with a certain dialing rule.
A phone number consists of an area code and a (subscriber) phone number. The first digits of the phone number are known here as a prefix.
Area code
Enter the area code which is to apply for this rule.
List of prefixes
Here you can enter a list of prefixes. If one of these prefixes matches the number to be dialed this rule applies.
Example
A phone number which fulfils this rule reads: +1 (202) 333-5678
Enter 202 as the area code
Enter 333 as the prefix
Version R2