Hello,
Thanks for trying to solve this mystery with Windows 7 and the Dial-up connection properties area code drop down list associated with it. Unfortunately, the information you suggested did not work. Step 4 and 5 are incorrect. Also, there is a bug in Windows 7 and the Dial-up connection properties area code box (Leave that box empty) put the (area code) prefix-phone number in the phone number box when setting dialing rules. There is a way to clear that drop down list I can't remember how to do it.
P.S. That is my post on another forum.