All of my old text messages disappeared. What might I be able to do to recover them?
Unless you have a previous backup, there's no easy way to recover them.
Use Handcent or GoSMS - they have in-built scheduling to backup SMS to your SD card or to send the backup to an email mailbox you specify.
SPOILER: The following does only work on rooted devices!
If they are already gone, in most cases it's too late. However, some chances are left if your device is rooted -- but they are not that easy to achieve: You would need a complete (physical) file system copy from your internal storage, and pull that to your workstation. Once you've achieved that, you can use a process called File Carving to get hold of even deleted files. This might get especially tricky as most devices use YAFFS2 for their internal storage -- a file system rarely used on any workstation.
Some File Carving software solutions include:
Concerning this special case (especially with YAFFS2), I'd say the best approach would be to go with a
Not everybody's easiest way, I know -- but there's no "easy solution" I could see.