That's right, Activision has finally announced officially that Guitar Hero: On Tour is in fact a portable version of Guitar Hero that is to be released on the Nintendo DS. The game will come with two peripherals: one is a pick style sytlus, and the other is four button (unlike the usual 5) fret board.
Now, all I've seen are the pictures here so I'm still not too sure on how it will all work together, but I'm sure it will be fun. The game is also said to feature the most diverse set list of master tracks ever offered in a Guitar Hero game and will include classic rock, alternative, and pop songs. (Hooray for master tracks!) Oh, and most importantly, there will be online multiplayer battles as well as local. :) I'm looking forward to it.
-CA