About two months ago, something happened on my AT&T Tilt2 Windows Mobile 6.5 phone. It showed that I had an unread text message in my inbox, but even after emptying all of the messages from my folders, it still showed that I had an unread message. Not a deal breaker, but certainly an annoyance.
A quick search on Bing and found this file: http://rapidshare.com/files/336446282/FixUnreadCount.exe. Run it on your phone, and viola! It’s fixed. Note: You might have to restart your device, but this avoids having to do a hard reset and losing all of your settings.