North American area codes can't start with the digit '1' because of numbering conflicts.
For example, in places like Atlanta and Dallas, you must dial the area code and number without the prefix '1' for all local calls (e.g., 404-555-0123). Also, for the benefit of people with rotary or pulse telephones, "star codes" can also be dialed by replacing the star with 11 (e.g., *70 for cancel call waiting can also be dialed as 1170).
If area code 170 existed and you dialed 11705550123, the telephone switch (in a non-overlay area) wouldn't know whether you were dialing 1170-555-0123 (a local number with call waiting turned off) or 1-170-555-0123 (a number in a different area code).
The 7-digit subscriber number cannot begin with '1' for similar reasons.
Area codes cannot start with a 0 or 1 in the North American Numbering Plan.
The North American area code system started in 1947. Missouri originally had just two area codes, 816 for the western half and 314 for the eastern half.
There is no area code 071 in North America. North American area codes never begin with zero.
Area code +44 121 is Birmingham, England, United Kingdom There is no North American (US, Canada, etc.) area code +1 121; North American area codes never begin with 1. There are several +1 21X area codes, all in the US.
There is no area code 139 in North America (USA, Canada, etc.). North American area codes cannot begin with 1.
There are several dozen area codes beginning with '9' in North America. See the list in the related links. It happens that, except for area codes 902 and 905 in Canada, all North American area codes beginning with '9' are in the United States. (as of 2012-05-29)
Livonia, Michigan, is in North American (country code +1) area codes 734, 248, and 947.
Some Caribbean countries have North American area codes. Others have their own country codes. For example, Jamaica is North American area code +1 876, but Haiti is country code +509. See the related links for details.
North Dakota has two area codes: 701 and 605.
The area code 215 is the North American telephone area code for the Commonwealth of Pennsylvania. The area code 215 was one of the original area codes established in 1947.
In North America (USA, Canada, etc.), area codes are randomly distributed; in fact, in most cases the people who assign area code numbers deliberately avoid placing similar codes near one another. Thus, area code 757 is in Virginia, but area code 758 is the Caribbean island nation of St. Lucia. See the related link for a list of North American area codes beginning with 7.
North American area code 829 is one of the three area codes for the Dominican Republic. Calls from the United States to area codes 809, 829, and 849 will incur international call charges.