My iPhone 3G has started showing random “phantom” voicemails from “Unknown” dated 1st January 1970. There are three empty voicemails, 0 seconds long and they cannot be deleted.
Actually that’s a lie, they can be deleted and they go into the deleted messages folder, you can also clear the deleted messages, but as soon as you go back to the main voicemail screen they re-appear instantly.
Powering off and on doesn’t resolve the issue, I’ve not tried a force reset yet or last resort full restore.
A quick search of the web reveals many others have been having this problem over the last year, but as of yet I’ve not seen any explanations or resolutions.