Start by right clicking on "My Network Places"
Then left click on "Properties"

Right click on your dialup connection
Left click on "Properties"

On this page you want to click on the "Rules" button

Then click on "Edit"

Click on the "Area Code Rules" tab

Highlight the current area code in the white box
Then got to "Edit"

Only enter the area code if you use
10 digit dialing.
Enter your area code and be sure to click on
"Include the area code" (If necessary)