The 747 area code overlay goes into effect for the San Fernando Valley beginning April 18. With the number of cell phones, Blackberry devices and fax machines increasing it was expected that the numbers using the 818 area code will be used up by the end of 2009. Using a new area code throughout the entire Valley, also known as an overlay, was done so as to minimize the impact to businesses and residents. The other option was to split the Valley in two between the 818 and 747 area codes. Customers with 818 numbers will keep them, although they and other customers will need to dial all 11 digits to make a local a call. That will require residents and businesses to reprogram cell phones, fax machines, speed dialers and call-forwarding numbers. The 818 area code extends from Glendale west to Westlake Village, Agoura Hills and Oak Park.