Simon over on Game Set Watch points out that New York-based game importer NCSX is raving about DS guitar "game" Utaeru DS Guitar M-06
With 16 chords to use at any time from a library of 120, users may strum out a song relatively easily if you're familiar with basic guitar playing. We were able to play the Main Riff I for "Fast Car" by Tracy Chapman and "Torn" from Natalie Imbruglia this morning by following guitar tabs found on the web. In addition to its function as a guitar, the software also includes a library of 20 songs and a listening-then-repeating exercise."
"On the touch screen, a thick crop of vertical lines represent the guitar string. It's pasted against a black background so that the focus is the line itself. To play, strum the line with your touch pen or finger and you'll hear a twang. Change chords with the D-pad by moving it in the direction of the chords shown on the top screen and the tone of the twang changes every time you move the D-pad to another chord."
I'm not so sure about changing chords with the D-pad, but I'm loving the rest of this.
Your DS Is Now A... Guitar? [GameSetWatch]