Is it all of the messages or is the problem sporatic? I have had this problem and it was sporatic where the thread of text messages would be there and only missing a few of them. I powered the phone down, took the battery out and then restarted it. It has been good after that. That would be my only suggestion.
I can imagine how upset I would be if my text messaging suddenly stopped. Let's look into this quickly for you.
Does this happen everywhere or just at one location? Have you made any changes recently to the features on your account? Have you tried the suggestion from CLdoc about removing and reinserting the battery?
Let me know if you are still experiencing this issue.