To my knowledge, there aren't any official national philanthropies for TBS, but I could be wrong. I know a couple chapters have taken on some local cause, though (i.e. saving money for band instruments for local school music programs, helping support a music festival for kids, etc.). Mostly, though, TBS has been focused specifically on the local college/university band programs (marching, pep, concert, etc.), and being of service to them.
granted, I'm a few years out of college now... and our chapter was in focus-on-survival-only mode for two out of my four years of college. I'd have to wonder how karaoke would go over with my chapter... I've often heard the joke that there's a reason we all play instruments-- we can't sing!
~ Mel.