From the website:
iHUD is an application (app) that turns the iPhone and - with limited features the iPod touch *) - into an aerospace-inspired mobile Glass Cockpit. iHUD derives its name from Head-Up Display, which depicts motion and flight-related pertinent guidance information and data for optimal situational awareness.
iHUD depicts an extraordinary graphic interface with a simulated horizon and a vehicle reference symbol, dynamic speed, altitude, and vertical velocity ribbons and digital display window, rotating compass card with user selectable heading bug, slip/skid ball, and an accelerometer (G-meter).
WOW that alone is worth getting an iphone