Okay so it doesn't exactly sound like rock and roll, but a new cable system GuitarBud that lets you plug your electric guitar into your iPhone is bound to please geeky guitar-players.
Made by Paul Reed Smith Guitars, GuitarBud lets you link your instrument up with lots of different apps. Hook up to simple Voice Memos to record a quick riff or use one of several apps for guitar player on the iPhone:
PRS have released their own free app to go with the cable - JamAmp app - a guitar amp simulator, tuner and training tool all in one. It also allows the user to change the pitch and speed of playalong tracks independently enabling tracks to be matched to the pitch of the guitar. Some of the other apps suited to use with the Guitarbud include StompVox, Riff Raters, GigDaddy, iStrobosoft, Rectools Pro and Guitar FX Deluxe.
Yes go forth and create geek musicians. Just don't go thrashing your guitar around - you might damage your iPhone...
Guitarbud, £29.95 from PRSguitars