If the Voicemail icon on your device's desktop is not displaying the number of unread messages, you can try to fix this by replacing the icon.
To replace the Visual Voicemail icon on your device's desktop, follow these steps:
1. Delete the current icon from the device desktop.
2. On the screen where you wish to place the icon, press and hold a location.
3. Click Widget (or Android Widgets) and select Visual Voicemail.
For further Visual Voicemail support, go to the customer care page on your service provider's web site.