Voicemail messages that reside on the phone company's servers expire after a certain period of time (5 days for Read messages and 20 days for Unread messages). The expired messages are deleted automatically from the phone company's servers. Once a voicemail message is deleted, there is no way to recover it.
You can, however, save messages on your phone by moving them to an Archive folder. The Archive folder has a limit of up to 500 messages or the available free space, whichever limit is reached first. If you reach the limit for the Archive folder, you'll see a message prompting you to delete some messages to make space.
You may also archive messages by forwarding them to an email address. There is an Auto-Forward to Email feature for Premium service subscribers that automatically forwards messages to a designated email address.
For further Visual Voicemail support, go to the customer care page on your service provider's web site.