How can you retrieve deleted text messages from the Casio GzOne Boulder?

Specialist data retrieval companies can pull deleted messages off your phone, but it's not cheap and there's a very high chance that the memory used to store the missing messages has been overwritten with fresh data.

Your phone service provider may hold a copy, in many countries they are legally required to do so. But it's data which is only usually released to governmental agencies and police. You may need a court ordered subpoena before they let you have a copy of it. If you do have this document, contact your carrier and make a request to get a copy of your messages. source