Threaded SMS is a part of OS 5. There is no way to disable it.
__________________ The difference between stupidity and genius is that genius has its limits. When you take things for granted, the things you are granted, get taken. Even a mosquito doesn't get a pat on the back until it starts to work. Too many people miss the silver lining because they're expecting gold. [BES 5.0.3 / GroupWise 2012 HP2]
In the first place people will always complain no matter whqat, if its black they want white, if it is vanilla yes it is chocolate.
If you can stand it get another phone, I hear the droids are doing good.