Why 10 digits in a Phone Number ??

The telephone number that you dial to call somebody is basically an address, similar to the IP address of a computer or the street address of your home. The length of the telephone number varies depending on the country you are calling.

In the United States, phone numbers are fixed-length, with a total of 10 digits. The 3-3-4 scheme, developed by AT&T in 1947, uses three blocks of numbers arranged in two blocks of three and a single block of four digits.


* Area code - Regulated by the Federal Communications Commission (FCC), area codes are used to designate a specific geographic region, such as a city or part of a state.

* Prefix - The prefix originally referred to the specific switch that a phone line connected to. Each switch at a phone carrier's central office had a unique three-digit number. With the arrival of computerized switches, many systems now allow local number portability (LNP). This means that a customer's phone number can be moved to another switch without having to change any part of it, including the prefix, as long as the customer does not move out of the local-rate area.

* Line number - This is the number assigned at the switch level to the phone line that you are using. Since the number is assigned to the line and not to the phone itself, you can easily change phones or add more phones to the same line.