A payphone can be located by carefully studying different parts of the telephone number. A telephone number is an address similar to the I.P. address of a computer. It has groups of digits representing geographical information.
All telephone numbers in the U.S. are 10 digits long. The telephone numbering scheme, called the 3-3-4 scheme, was developed since 1947. It provides extensive geographical information. The first three digits form the caller's area code, identifying the city, or part of state. The second three-digit group denotes the prefix, which represents the switch or telephone exchange to which the number is connected. The next four digits represent the individual subscriber line. So, using the three parts, the payphone number gives the city, street and the number of the actual payphone. By determining in which direction the numbers are increasing, a good estimation of the payphone's location can be made.