The Canadian Radio Television and Telecommunications Commission (CRTC) approved a new area code in June, 2014 as the relief method for overlay complex 519/226 – the two area codes which currently serve the southwestern part of Ontario, Canada. Some example cities using these codes: Kitchener/Cambridge/Waterloo region, Guelph, London, Windsor, etc. The new area code 548 will also cover this same area starting June 4, 2016.
Communities in this part of Ontario have been using 2 area codes since 2006, when area code 226 was overlaid on 519, which means that 10 digit dialing is already required when calling locally. The addition of a third area code will therefore have no effect on how calls should be dialed when NPA 548 enters service next year.
See official NANPA announcement and area code map of 519/226/548 (PDF document)