I've had my 8830 (Sprint) for a couple months now. Never had any troubles until Monday. I happened to check my text messages, and they were all gone! For the next day, I couldn't receive any text messages. Then, for a couple hours, I could get a few, and now again, I can't get any. All previous texts were deleted. I also noticed that my call history has been erased as well.
There have been a few posts regarding this lately. Go to Options>Status and check how much memory you have available. Apparently if you run low on memory then the device starts getting rid of your messages/call list etc to make some room
EDIT: Should also add, check what applications you have running as they eat away at the memory. If you do a battery pull it should clear some memory up for you