The 289 area code is an integral part of Ontario's telecommunications system in Canada, serving a substantial portion of the Greater Toronto Area and the Niagara Region.

Introduction as an Overlay: The 289 area code was introduced as an overlay to the existing 905 area code. This overlay was implemented on August 13, 2001, to address the exhaustion of available phone numbers in the 905 area code due to the rapid population growth and the increase in telecommunications devices. The overlay approach allowed existing 905 number holders to keep their numbers, while new numbers could be assigned the 289 area code.

Geographic Coverage: The 289 area code, along with the 905 area code, covers a significant portion of the Greater Toronto Area, including suburbs like Mississauga, Brampton, and Vaughan, as well as the Niagara Region, encompassing cities like Hamilton, St. Catharines, and Niagara Falls. This area represents a mix of urban, suburban, and rural landscapes, reflecting the diverse demographic and economic composition of the region.

Implementation of Ten-Digit Dialing: With the introduction of the 289 overlay, ten-digit dialing became mandatory for all local calls within the 905 and 289 area codes. This requirement, which necessitates dialing the area code followed by the seven-digit phone number, aligns with the standard practice in regions with overlay area codes across Canada. The shift to ten-digit dialing was essential to manage the growing number of phone users and the consequent need for more telephone numbers in the region.

These facts about the 289 area code highlight its vital role in supporting the telecommunications needs of a substantial portion of Ontario, particularly in the densely populated and economically significant areas surrounding Toronto and in the Niagara Region. By providing additional numbering capacity and facilitating the transition to ten-digit dialing, the 289 area code ensures that the region's communication infrastructure can keep pace with its growth and evolving needs.