How to change phone number format (1-xxx-xxx-xxxx) in Address Book?

I am running 10.4.11 on my Macbook Pro and wish to make my Address Book phone numbers consistent by adding the "1" before the area code. It states in the help area that I can change this via the Preferences. However when I do this, it doesn't change the numbers in my Address Book that currently do not have this configuration.

How do I get all the xxx-xxx-xxxx formatting numbers in my Address Book to read 1-xxx-xxx-xxxx without having to do so manually? Thanks.