Ranges for fictitious telephone numbers are common in most telephone numbering plans. One of the main reasons these ranges exist is to avoid accidentally using real phone numbers in movies and television programs because viewers frequently call the numbers used. In North America, the area served by the NANPA system of area codes, fictitious telephone numbers are usually of the form (XXX) 555-xxxx. The use of 555 numbers in fiction, however, led a desire to assign some of them in the real world, and some of them are no longer available for use in fiction. Other areas have different fictitious telephone numbers.