I understand their problem. When you go into the visual vaoicemail app for the first time is asks you to upgrade. When you click yes it will say downloading but it will say that FOREVER! I can't get mine to download it.
Mine was doing that two days ago...for some reason, yesterday I tried again, and it downloaded no problem. I didn't do anything different, just tried again.
The solution is to go into Settings>Application> set it to allow 3rd party non-Android apps. Once you set to okay you will be able to download the voicemail update.