If you have those messages in a saved backup file somewhere on your computer you'll be able to retrieve them. Otherwise you're out of luck.
FIXMO TOOLS doesn't even give the option to "undelete" SMS/MMS. It can only "undelete" and restore emails, contacts, pins, etc. that you have accidentally deleted. While it won't help in this case, it will help make sure you're not in this situation again with regards to emails and the likes. Download the free trial!