1200 W. Washington Street

Phoenix, AZ 85007-2927


Phoenix Office: (602) 542-4251


Tucson Office: (520) 628-6550


Toll Free In-State Only:

1-(800) 222-7000

All About Area Codes Answers to Common Questions

What is an area code?

Area codes were first developed in the late 1940s in order to meet the post-World War II surge in demand for telephone service. An area code consists of 792 possible prefixes; each consisting of 10,000 numbers (all the possible combinations from 0000 to 9999). A prefix can begin with any number other than 0 or 1 and cannot end with 11 (as in 911 or 411 -- these are reserved for special uses). This is how we end up with only 792 available prefixes.

Numbers currently are allocated to telephone providers by prefix. As these prefixes are assigned, there are fewer remaining numbers to be given to new providers.

Who oversees the assignment of area codes?

The North American Numbering Plan Administrator (NANPA) tracks the consumption of numbers and assigns new area codes as necessary. NANPA has notified the telecommunications industry and the Arizona Corporation Commission (ACC) that the 520 area code is expected to run out of available numbers by late 2001.

Why do we need new area codes?

The 520 area code is running out of available telephone number prefixes. Competition and new telecommunications providers entering the market are consuming the available prefixes. In addition, the rapid proliferation of cellular phones, pagers, fax machines, modem lines and Internet-based enhanced services is accelerating the use or consumption of these numbers. Many homeowners are opting to have two or more phone lines installed in their homes and businesses are adding phone lines at a brisk pace. All of these factors mean that there are fewer and fewer numbers available.

Why can't you assign the new area codes to pagers, faxes and cell phones?

The Federal Communications Commission (FCC) will not allow a specific area code to be assigned to pagers, cellular phones and faxes. FCC rules prohibit the assignment of numbers based solely on a group's specific type of telecommunications service or the use of a particular technology.

Who decides which areas receive the new area code?

The Arizona Corporation Commission (ACC) makes the final decision. NANPA notifies the telecommunications industry when a particular area code is projected to run out of prefixes. Telecommunications providers begin meeting to identify possible solutions to the problem. The industry then brings their recommendations to the ACC.

So what are the options?

There are two options for implementing a new area code: a geographic split or an overlay.

What is a geographic split?

A geographic split essentially draws a line through an existing area code and assigns a new area code to customers on one side of the line. The other side of the line would retain their existing area code. This requires many customers to change their telephone numbers and distribute the new number to all of their contacts. Businesses will have to reprint stationery, business cards, brochures, checks and other printed materials. Residential consumers will need to alert their friends, family and businesses they use to let them know the new area code.

What is an overlay?

An overlay adds a new area code to an existing geographic region. This means that two area codes will work in the same general area. New customers would be assigned the new area code. In some circumstances, customers may be able to choose between the old area code and the new one.

How are customers affected by an overlay?

All existing telephone numbers will remain the same. Businesses don't have to reprint their stationery, business cards and brochures unless they are adding a new public phone number. Adding an overlay code means that you will need to dial all ten digits of a phone number to complete a local call. The ten digits include the area code plus the 7-digit number.

Will I be charged toll rates for calls to the new area code?

No, not if the call was a local call before the new area code was introduced. Calls that are toll calls now would remain toll calls. For example, calls from Tucson to Phoenix would still be toll calls. 
By law, call rates cannot be increased solely as a result of an area code split.

Will I have to change the way I dial emergency, directory assistance or long distance numbers?

Emergency dialing and directory assistance would not be affected. You would simply dial 911 or 411 as usual. You would still dial 1 + area code + seven digit number to complete a long distance call.

How is a new area code implemented?

Implementing a new area code involves two steps designed to familiarize phone users with the change. The introductory period is called "Permissive Dialing" which begins with the introduction of the new code and lasts several months.

  • With a geographic split:
    • Permissive Dialing allows the old and new area code to be used interchangeably.
    • The second phase is called "Mandatory Dialing" at which time callers must use the correct new 10-digit number to call numbers outside their area code. Local calls within the same area code can be completed by dialing only the 7-digit number. Callers who do not dial the proper number will hear a recording announcing the change.
  • With an overlay:
    • A Permissive Dialing period is also used with an overlay and allows the customers to begin using 10 digits even though the calls will go through if only the 7-digit number is dialed.
    • Once Mandatory Dialing starts, callers are required to dial the 10-digit number on all calls. Callers who do not dial the proper number will hear a recording announcing the change.

What are some of the pros and cons of a geographic split?

Pro: Ten-digit dialing is necessary when calling another area code or when making a toll call.

Pro: Area codes have a geographic identity. People can get an idea of where a business or individual is located by looking at their area code.

Con: Existing telephone numbers change -- approximately half of the people have to change their telephone numbers. Each time there is a geographic split, businesses have to pay to reprint all of their literature, promotional items, stationery and business cards to include the new number.

Con: As more and more numbers are used up and as the state continues to grow, the "slicing and dicing" of a specific area will continue. Geographic splits are not long-term solutions and future area code relief must be undertaken. For example, the Chicago metro area used to be served by just the 312 area code. Now they have this arrangement:

  • 312 = Downtown Central Chicago
    773 = Remainder of Chicago
    847 & 224 = Northern Chicago suburbs
    708 = Southern Chicago suburbs
    630 = Central Chicago suburbs

What are the pros and cons of an overlay plan?

Pro: Only new customers or businesses or individuals requesting new lines get the new area code. All existing telephone numbers remain the same. No one has to incur the costs of changing their printed material.

Pro: An overlay may be a long-term solution since an overlay would be used in future numbering exhausts. New area codes are simply placed over the affected area with each impending exhaust.

Con: People have to get used to dialing all 10 digits all of the time. The exception is when you dial special use numbers like 911 for emergencies or 411 for directory assistance -- these do not require an area code.

Con: Businesses and individuals will need to reprogram certain phone systems, burglar alarm systems and other equipment to accommodate 10-digit dialing. Businesses and individuals may have more than one area code for their lines.

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Arizona Corporation Commission

1200 W. Washington Street

Phoenix, AZ 85007


Corporations Division

1300 W. Washington Street

Phoenix, AZ 85007


Tucson Office (Walk-ins only)

400 W. Congress Street

Tucson, AZ 85701