Apparently, Microsoft and Bungie are providing new methods on getting onto the Halo 3 beta:
http://www.themoneytimes.com/articles/20070104/microsoft_and_bungie_studios_provide_new_ways_to_join_the_halo_3_beta_test-id-102615.html
On a related note, it's kind of disappointing right now that it is almost impossible to play multiplayer Halo on Starhub these days as the connection is simply too bad.
