I have an app called G Backup Full (Full Version = $) that can backup SMS, MMS, Call Log, Images, and Videos as archived gmails with custom labels, i.e. Droid SMS, Droid MMS, etc. I have it set to backup SMS, MMS, and Call Log automatically and it usually is pretty quick (within a minute or so). This way I know everything is backed up all the time and can clear out my messaging inbox with confidence when I need to. I also have an app doing (redundant) nightly backups of the same stuff to the SD card (Although it does back up some different things, i.e. general settings, home screen layout, etc). That one is MyBackup Pro (again Pro version = $). Anyways, G Backup has quickly become one of my favorite apps and I have yet to have any trouble with it aside from it freezing occasionally when doing the first backup of my messages, but to be fair there were several thousand, lol.