One way to discover what area code goes with a phone number is to use the website AllAreaCodes.com. This site can help you discover areas by phone number as well as browse area codes to learn which areas are associated with which numbers.
On the home page of AllAreaCodes.com is a Reverse Phone Lookup search box as well as an Area Code Lookup search box. If you have the full phone number, use the reverse phone lookup feature to discover the approximate location of the number. If you only have the area code, use the area code lookup feature. When searching by area code, the website returns details for the state and cities with which it is associated, including the most prominent city.
If you need to know the area code associated with a caller's area, you can use the Area Code Listings By State feature on AllAreaCodes.com. This lets you browse a state's area codes and click on them to reveal information about the cities that use each code.
A final option is to browse the website using area codes ranging from the 200s to the 900s, which can help you narrow incoming calls down to the state and approximate area.