Dialing USA
The other type of code is USA National Direct Dialing prefix (or NDD). It is used only when dialing to a destination within the USA. USA NDD code is only used as long distance dialing within the USA. Do not use USA National Direct Dialing prefix when dialing from outside USA into USA.
For USA long distance, you have to dial USA National Direct Dialing prefix (or NDD), City/ Area Code, and then the subscriber telephone number respectively as:
1 (USA National Direct Dialing prefix code) + City Area Code + Number you wish to call.
On the other hand, International Dialing USA Code or USA International Direct Dialing prefix (or IDD) is used when dialing from the USA to outside USA. Do not use USA IDD code when dialing within USA for long distance.
On the other hand, when dialing to USA from outside USA, a USA Country Code is used . USA Country Code however is not used when dialing within USA.
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