My wife and I both have MT4Gs with Visual Voice Mail enabled. Hers started failing with a message android.process.acore has stopped unexpectedly. Mine was still working fine. To fix it I went to Settings | Applications | Manage Applications | All. I scrolled down to Visual Voice Mail and selected Clear Data. I then went back to the home screen and touched the handset icon. I selected Voice Mail and was prompted to enable Visual Voice Mail. I did so and it works again. Hope this helps some of you.