Nokia 6255i / 6256i

My phone number is area code 631. When someone calls me from a number also in area code 631, their number is displayed with area code 631. All local calling numbers (same area code) are listed in my contacts without area code. When those people call my phone their number is displayed (with area code) Because the incoming number displays the area code it does not match the name in my phone book. How can I change this? Will I have to add an area code to every number in my phonebook, even though we share the same area code, just so I can have their name displayed when they call? Is there a workaround for this?