If your like me and would still like to play Halo 3 online, or want to be prepared for the slight chance the beta doesnt last till the new game. When you switch back to Halo 3 change your controller settings to walkie-talkie it is the same set-up as the Reach Beta only X and B are flipped (X on reach reload, X on Halo 3 switch grenades, and B on Reach reload, B on Halo 3 reload)

beta's only open for 17 days bro, heaps will go back to halo 3,
also if your not liking the buttyons layout for reach, you can swap it to the "recon" layout and its pretty much the same as halo 3 except X is switch grenades and LB is to use an armor ability, hope this helped ^^