When there's a risk of an area code running out of phone numbers, an 'Overlay Area Code' is created that has the same geographic boundaries as the existing area code. In this case, the 450 code has been Overlayed with one of the following codes: 354 or 579. New phone numbers in the Hemmingford area will be assigned with one of these codes: 450, 354 or 579. As a result, placing a call in the Hemmingford area will require 10-digit dialing (where you enter both the area code and then the phone number).