I've had this problem on my iphone4s only after the latest ios update. Whether its att(carrier) or apple, they both get to share the profits, therefore they both get to share the problem. Although I've tried all of the suggestions above, with limited and temporary fixx, the problem still persists, not only do i get the visual voicemail unavailable, forcing me to "call voicemail" to get unheard messages, but the voicemail icon doesn't update correctly and gives the impression there are still unheard messages. This is what I've found...after trying all the above, you may still have to go to the App Store, check for app updates( even the non-apple apps) ...download and install the updates and get this.....open and close each and every update for them to properly apply before the total reset thing will actually fix all the problems. If you're having the same symptons...you will probably be surprised with missing messages when the visual voicemail becomes visible, and your voicemail list will give accurate count of messages heard and unheard. This is also important because merely "calling voicemal" doesn't tell you when a particular message was left, and the visual voicemail does.. and by the way, It will happen again and again till APPLE/ATT get it fixed on their end. Is this just another ploy to get people to boost ATT bottom lim line by tricking/forcing users to call voicemail an excessive amount of times....when I listen to a message by calling, and choose 7 to delete the heard message, the list doesn't reflect that this has been done, thus forcing users to double check by calling again...this is confusing and cruel to the ederly, newbie or seasoned user who hasn't discovered the fixes and are racking up unnecessary call minutes and wasting time. But a typical example of bad business and reputations in a competitive phone market...