The phone numbers in the US have the following format:
Area Code (3 digits) + Exchange (3 digits) + Root (4 digits).
Example: 123-456-7890
When you call a number that\'s not in your area code then you always dial 1 + the number so the example above would be: 1-123-456-7890 (presuming you\'re not in the 123 area code).
However, when you call from overseas, I think, you skip the \"1.\"
Additionally, when you\'re in a smaller town / rural area and the phone number you\'re calling is within your area code you don\'t need to dial the area code. On the other hand, most larger metro areas have multiple area codes (but the calls to those are still considered local as opposed to long distance, i.e. \"out of your area code\") so you must dial all 10 digits (including the area code) but not the preceding \"1.\"
I hope that this helps...
(or at least that I didn\'t confuse you too much...)