Violin God is a parody of Guitar Hero on the TV screen.
Dan Schneider often calls this game "Violin Hero." He also says that "if you look closely at Miranda's fingers, you'll see that her red violin actually has the same kind of buttons you'd see on a guitar from Guitar Hero."
Fun Fact: In the original version of iSaved Your Life, an error was made because you could see the notes being played after Carly stopped playing. This was fixed in the extended version (as mentioned in Danwarp's fun facts).
Also, in iTake on Dingo, some of the writers were playing it.