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All of these solutions are a lot of work. The easiest way is to use Bulk Rename Utility and VLC player which are both free for this purpose. In Bulk Rename Utility navigate to a copy of the backup file in the menu on the left. select all files in the box on the right. In the seventh box "add (7)" there is a box called Suffix. In the Suffix box put in ".amr" (without the quotes). then hit rename. All the files should have the suffix .amr now. Open the files in VLC player files with duration are either videos or the voice mails. Only problem is you have to sort through them yourself.