what is area code 289
289 Area Code Information. Area code 905 (with overlay area codes 289 and 365) is a telephone dialling area in southern Ontario, Canada. It includes the Niagara Peninsula, Hamilton, Oshawa, and the suburban greater Toronto area.It was assigned on 4 October 1993, as a split from area code 416.289 began sharing the service area on 9 June 2001, since then, all local calls require ten-digit dialling.t was assigned on 4 October 1993, as a split from area code 416. 289 began sharing the service area on 9 June 2001, since then, all local calls require ten-digit dialling.