I backed up /system/app/Mms.apk with Titanium Backup Pro, and then un-installed it, because I use handset as my main messaging app. However, after uninstalling, handset is unable to send/receive MMS messages.
Titanium is unable to restore the app, it just sits there and I have to shut it down. I had to restore the Mms.apk/.odex from the partition dump provided in another thread.
So Titanium users, be forewarned...