Because telephone area codes are designated according to location, in order to find an unknown area code you need to know the name of the location where the person you want to call activated their telephone service. For landline phones, this location corresponds to the physical address (town and state) where the person or business you want to call resides. For mobile phones, identifying this location is trickier. A person may have activated their cell phone in Miami, Florida, for instance, but may actually now reside in Richmond, Virginia, in which case their area code will correspond to Miami, Florida.
Look in the introductory section of your White Pages phone book. You will often find a detailed listing of all of the area codes for the towns in your state and a general listing of the area codes assigned to all the other states in the U.S. This general listing likely won't include a rundown of all the towns which fall under a particular area code; it will probably just list the major town or city assigned to each area code. If you're trying to find an out-of-state area code using a local White Pages phone book, use the area code belonging to the closest major town or city to the location you're looking up.
Call directory assistance (4-1-1). Tell the operator the town and state of the telephone area code you want to know. Then ask the operator to provide you with the area code for that location. Be advised that some telephone plans charge a small additional fee for directory assistance phone calls.
Use one of the free area code lookup tools offered on websites like the White Pages online or Verizon online (see the links in the resources section of this article). Again, you need to know the town and state of the telephone area code you want to look up in order to use this tool.
You can take a cell phone anywhere. Therefore, when you call a person's cell phone number the area code may or may not correspond to where they currently live. Remember, in order to find an area code you have to know the location where the person you want to call activated their telephone service. If a person's cell phone was not activated in the town and state where they currently resides, try looking up the area code for their hometown, or the place where they went to college, or where they used to work. Many cell phone users retain ties to former places of residence through their area codes.