Area code is use to setup Dial Up connections. However, this is not required
if your ISP is located in your local area but Windows will not let you left
it blank. But later, you can uncheck the "Use Dialing Rules" from your
Connection Properties if you don't want to include Area Code while connecting
your ISP. Further, there is no need change Phone and Modem options if you
have a Broadband connection.
This entry is store under Registry Editor. Take a look at:
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Telephony\Locations\Location1
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