Download an alternative one from the market? hancent, chompSMS, Go SMS are all good. Or, factory reset. I cannot help you further (and my advice may be wrong) because I am not familiar with that phone.
Also, please read the forum rules and look through the forum for your appropriate phone sub forum. This subforum (for Computers and IT) is not the appropriate place for you question. IF you were to post in the right place (or even an Android general place), you would find people who have your phone and know how to help. It would both expedite your answer and keep the forums organized--a win-win situation,
Yeah Nkk is right, they'll be able to help you immediately if you post in someplace else. Or were you posting here because your phone isn't listed? That isn't likely, maybe you just don't know your phone's title, but even a forum for a device with the same manufacturer would be more helpful (but don't do that, go to general like Nkk said if you don't know the name. also, TRY to find the name first; you should be able to, right? Narrow it down by your carrier) because they might know about that update. I mean, that's a pretty serious problem, it wouldn't fly under the radar.
Let them know:
-the NAME of the phone
-if your phone is rooted or not
-if YES, rooted, what other changes were made to the stock OS
-how you updated to 2.2
Also, handcent is (probably? maybe?) the most popular messaging app, so if you have trouble deciding, might wanna start there.