What is the phone jack for on the Guitar Hero III guitar?

no one knows yet, there are many rumors going around for what it can be for, but still no definite answer. Probably some extra peripheral they plan on releasing in the future.

It’s so you can call your agent before you play a show.

It’s all speculation on my part, but I’d guess it’s for a pedal board peripheral with distortion and wah-wah, delay, possibly some other things, in which you have to choose the appropriate effects for the right time in the songs to get more points or even to get any credit for the notes.

I believe that the phone jack is for a cable that connects the controller to the console for wired gaming.