HTC Sense and its new type of messaging software has had constant problems with slowdowns and freezes ever since its release. Well, a thread which has recently emerged, has had some rather heavy traffic over in the HD2 Leo section and it may just have the fix you are looking for. Some newer versions of the HTC messaging client have been posted over there, even the newest one from the latest ROM release. With lots of reading and some tweaking, you can get some nice new features such as the one known as Secure Inbox! To top it off, there have also been many claims that the lag and freezes have disappeared in these newer versions.
You can find more information in the application thread.___________________