Sonic 2 will include the entire Genesis game, but with some slight edits for the smallest screen, such as an adjustment of the view of the playing field since few cell phones -- including the P902iS have the same screen ratio as tradition tube TVs. Even the between-zone mini-game where Sonic and Tails shoot the tubes is present. This is where you could pick some some major score bonuses.
Check out this first batch of screenshots to get a sneak peek at Sonic's next cell phone adventure (in Japan, at least).
Screenshots:

There are no current plans for the mobile game to arrive in America any time soon. How lucky for Japan!