Follow these steps to change your dial-up number in Windows XP.
1. Click on the Start Button and the Click on ‘Connect To’.
2. Click on ‘Show All Connections’.
3. Right Click on the Dial-up Icon and Left-Click Properties.
4. Left-Click on the ‘Phone number:’ dialog box and type in the new number appropriate for your area.
5. Click OK to save your changes.