My Curve 8310 has decided to do the same thing and a colleague also experienced this.
Sounds like a bug with Blackberry Curves, unfortunately mine is playing up 2months after the warranty expires so they won't replace it.
![Mad](http://www.blackberryforums.com/images/smilies/icon_mad.gif)
![BB Icon](http://www.blackberryforums.com/images/smilies/bb_icon.gif)
![Mad](http://www.blackberryforums.com/images/smilies/icon_mad.gif)
-wish my I.T supported HTC phones-