The website will help you track which mobile numbers are on DND.  
You can copy paste an entire excel sheet column containing mobile numbers and the site will give you details for all the mobile numbers DND and also if the number is a valid mobile number or not.
You can use the Target Segment All Guests to export such data and check to see how many of your guests will be on DND. This would be especially useful if you are running SMS Campaign for all your guests.

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