Originally Posted by falconey
If you simply root your phone nothing will be deleted from the hard disk.
Not deleted, but places where files used to be, and have been deleted from, CAN be overwritten when you root, even if you do it manually. One-click roots are even worse - most of them change some ystem files and make backups of the originals, so more of the "free space" gets overwritten, which means more chance of wiping out the very files he's trying to restore.
A full JTAG might be able to get into storage and find the data, but paying someone to sit and search through a few gigs of data looking for texts, on most young peoples' phones, would cost a fortune.