How can I fix my iPhone visual voicemail?
Some iPhone users may have noticed their visual voicemail stopped working after installing the 3.0 tethering hack. To check and see if you are not receiving your messages have someone leave you a message, then check voicemail manually.
To check voicemail dial your phone number directly from the iPhone. Press "1" to check messages. If you have voicemails waiting for you but no visual voicemail try this fix.
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.