If you are one of the iPhone users who has noticed their Visual Voicemail stopped working after installing the 3.0 tethering hack, then there’s still hope for restoring it back! To check if this is happening to your device or not have someone leave a message on voicemail and after listening through carefully ensure that all sounds should play without any glitches before checking manually in order to find out where things went wrong (more info below).
If you can’t see your Voicemail on the iPhone, here is a quick fix. Tap ‘1’ to check messages and if there are any voicemails waiting for you but no visual interface (like stars) then try this!
Navigate to your Settings. Touch Settings -> General -> Reset -> Reset Network Settings.
The iPhone will reboot and your visual voicemail should return to normal. This process resets the .ipcc (carrier settings) file that was altered in the tethering hack. Turns out the tethering hack has a side effect of disabling visual voicemail in this file.