Unity3d supports Touch, but is there a way to fetch the pressure of a touch on mobile devices?
iPhone/iPad has no such thing, in Unity or otherwise. I'm not certain, but I suspect Android doesn't, either.
Wrong, Garageband detects the pressure by accelerometer. Because when you tap hard on device it produces light motion.
Try to wiggle with your device during play and you receive higher “pressure”. This technique works quite well. used on aquarium when user taps on the glass the sound gets louder.
Touch pressure is now available on devices that support touch pressure feature.
You can check this using touch.pressure from your individual touches returned by GetTouches()