With this jailbreak tweak you will be able to recover deleted messages on your iPhone. The tweak is called “Undelete SMS” and it scrapes your SMS database or Spotlight history for deleted records and recovers them. All of your recovered SMS messages are displayed in plain text, you can copy the texts you want and stick them in a note, email, etc.
It shall be noted that while the “Undelete SMS” is a forensic recovery tool and it is not 100 percent guarantee that it will recover all or any deleted content. Another thing to note is that it will not work on a freshly restored phone without a backup.
So you can only use this jailbreak utility from an actively used phone.