Interestingly, the iTunes listing for GRT comes with the following warning: "GUITAR ROCK TOUR MAY CRASH IF YOU HAVE NOT REBOOTED YOUR iPHONE IN SEVERAL DAYS (as with all large iPhone apps)." Gameloft promises improved stability in upcoming updates.
GRT (US$7.99) requires the iPhone 2.0 software update. Caveat emptor: it's also not compatible with the iPod Touch.
[Available on iTunes]