It will likely be difficult. But, if you use the Desktop Software to back up your BB, you will have on your computer an IPD or BBB file (depending on the version of the Desktop Software you use). You then can seek out a 3rd party app for the PC that will parse that file into "human-readable" format, and perhaps allow you to then save the Messages database into a usable format.
Your next step would be figuring out how to perform an import of that into the Galaxy...which, I believe, would be a question more suited to Samsung forums rather than BlackBerry ones. Further, the Galaxy may well have their own "migration wizard" that would do all of this for you...but, likewise, that is a question more suited to a Samsung forum.
Occam's Razor nearly always applies when troubleshooting technology issues!
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