The 578 area code is one of the unassigned codes for the North American Numbering Plan, which includes the United States, Canada, some Caribbean countries, and U.S. territories. The use of a phone number with an area code of 578 is a way to hide where a call is coming from.
In the NANP, area codes were first used in the early 1950s. At that time, 86 of the 152 possible area codes were in use. As the number of phone users grew over the years, more area codes were added to meet the needs of higher-population areas of the continent. For example, in the New York City area, area code 917 overlaps with area codes 212 and 718 to make room for the large number of new phone users.