There may be a way to recover deleted text messages if you have a phone with a sim card. You want to do this ASAP before the data is overwritten. I don't know anything about the HTC but pasted a couple of links at the end of this reply that describe how to recover.
Also, for the future, you may want to download a text (SMS) backup app from the Android Market. I did a quick search of the market and found these backup apps: SMS Backup +, SMS Backup & Restore, TxtArchive SMS Backup, and backup SMS MMS Photo to Gmail. There are probably more text backup apps than these.
Here are some links that describe how to recover deleted texts if your phone has a sim card:
How Do I Read Deleted Text Messages?
How to Recover Deleted Text Messages from an Android SIM Card - Softpedia
There are also some companies that specialize in recovering information. Here is one ad from Youtube. They will need to know the make and model of your phone to be able to tell you if there is a solution: Can you recover deleted text messages from a mobile phone? - YouTube
However, you can find many companies that provide this service.
Hope this helps. Good luck.