You can "dissect" the phone number to better understand a caller's location. For example, the first digits represent the country of origin (the U.S. is '+1'). Next is the area code, three digits originating from a specific region or state (some states have several area codes while others only have one). After the area code, you'll find the Exchange code (the Central Office Code). This code is the three digits that follow the area code and represent a more localized zone within the area code region. Although not as useful today as in the days of regular landlines (POTS), the Central Office Code once gave users the neighborhood. Lastly, the four digits at the end of the phone number are a unique identifier known as the Subscriber Number.