I know they made On tour for the DS, but the touch is only used for Strumming and others, but not Fretting as I say. You guys should make a Guitar Hero Tap on the DS and DSI. This is where you tap on the corresponding color on the strike line. I know you can't really make Chords because you cant touch the screen simultaneously. If tapping sounds like similar games you could add a strumming accessory that or use the up and down.
They already have this game. It's called Guitar Rock Tour. You have 6 strings and you tap the string to play the note. To play chords, you slide your pick across the strings, like on a real guitar.
eww guitar hero can't try to make their game into a Tap Tap game like on the the ipods