The procedure for changing the phone number is roughly the same for all recent versions of Windows.  These step-by-step instructions are for Windows 95 but should be an adequate guide for any Windows version.

Start at your Windows desktop ...

• Double click on "My Computer"
• Double click on "Dial-Up Networking"
• Single click on your connection icon to highlight it

  Your connection icon may be named "NetHeaven" or something else. If you did not choose a name when your account was initially configured, the default name is "My Connection".

• Single click on the "File" heading
• Single click on "Properties"
• Enter the phone number
• Single click on "OK"
• Close the windows you've opened