There are a couple of ways that you can recover deleted messages from a cellphone. One is hardware-based, and the other is software-based.
The hardware-based method requires you to purchase a sim card reader device, which helps you find deleted messages from your sim card. You do this by plugging the sim card into the device, and plugging the device into your computer. This piece of hardware is called the Cell Phone Spy Data Extractor, and you can get it on Brickhousesecurity.com for $79.95. It's usually priced at $99.95.
The software-based method might be the better method, because the data isn't as time sensitive as the hardware-based method. You can use this method by installing the spy app to your phone. Try Spy Bubble, Spouse Spy, or Mobile Spy. It is not encouraged to use these apps and devices illegally.
Alex Morrison, of the Huffington Post, recently addressed the drawbacks of spy apps. He states that these spy apps are encouraging an invasion of privacy, especially amongst parents, jealous spouses, and employers. You can read the full piece here.