Area code 973

Area codes 973 and 862 are North American Numbering Plan area codes for Northern New Jersey that cover portions of Bergen, Essex, Hudson, Morris, Passaic, Sussex and Union Counties. Cities served by these area codes include Newark, Paterson, Clifton, Passaic, Montclair, Morristown, Parsippany, Dover, and The Oranges.

Area code 973 was formed on June 1, 1997 when the Numbering Plan Area 201 was split. The creation of 973 was intended as a long-term solution, but within three years it was already close to exhaustion due to the proliferation of cell phones and pagers.

To relieve this, area code 862 was created as an overlay to area code 973, making 10-digit dialing mandatory in the plan area since 1 December 2001. This overlay was rolled out in conjunction with two other overlays in the northern half of the state.

...
Wikipedia