You can retrieve messages that have been deleted recently. Follow these steps:
1. From your voicemail Inbox, tap the bar labeled Inbox at the top of the screen. This produces a list of locations that voicemail can be moved to.
2. Tap Trash. The list of all recently deleted messages appears.
3. Press and hold the message to be restored until the long press menu bar appears.
4. Tap the Restore to Inbox menu option
5. You can now return to your Inbox by tapping the bar marked Trash and then selecting Inbox.