Does this only happen when you're calling your voicemail, or do you have this issue with all phone calls? And just to make sure, are you sure you aren't locking your phone using the lock button at the top of the device? Assuming you've already checked these items, here is an alternative.
I'm going to suggest doing something a little extreme, and that is to reload the software on the device. This will help to rule out a software related issue. To do this, follow the steps in the following link:
http://supportforums.blackberry.com/t5/Device-software-for-BlackBerry/How-To-Reload-Your-Operating-S...That should work for you, but if not, it would suggest that the problem may be hardware related, in which case, I would take the phone into your carrier for warranty assistance.
I hope this info helps and keep us posted!
If you want to thank someone for their comment, do so by clicking the Thumbs Up icon.
If your issue is resolved, don't forget to click the Solution button on the resolution!
