Be easy! These are good solutions for this issue:
If you have already backed up your iPhone with iTunes, you can get the deleted text messages back by the following steps using iTunes:
Click the File menu and select Devices > Restore from Back up.
Open the iOS device's Summary tab. There are two ways to access this:
Click the device button in the upper right corner.(If viewing the iTunes Store, click the Library button in the upper right corner. The device button will then be visible.)
From any view in iTunes, click the View menu and select Show Sidebar. Select your iOS device in iTunes under Devices.
Click the Restore Backup button.
For iTunes 10.7 or earlier:
Right-click (or Control-click) the device and choose Restore from Backup
If haven't had time to back up your iPhone before the deletion, there are also two methods for you to try:
1. Recover the text messages directly using a third party data recovery software;
2. Recover the text messages under DFU mode.
I have found a detailed tutorial for you guys http://iphone-ipad-ipod-data-recovery.blogspot.com/2013/05/iPhone-sms-recovery.html
2 methods are introduced in this tutorial.