There are some wonderful piano apps on the iPad store. They can be great fun and sound incredibly realistic if connected to your home stereo system! Many provide a fantastic introduction to the theory of music and what each of the keys and combination of keys do and sound like on the piano. Some will teach you how to read music too. However, they all share one common but major problem. It is impossible to recreate the feel and feedback of a real piano on the iPad keyboard. There just isn't the room to use both hands on the screen if the simulated keys are the same size as those on a 'real' piano. However, it is possible to buy an external 'Midi' keyboard for as little as £25 which can be connected to your iPad via the 'Camera Connection Kit' (which can be bought from Amazon for as little as a fiver). These feel similar to the 'real thing', particularly coupled with an app such as 'Pianist Pro' (£2.99).
However, I can't help thinking that this advice is of no particular use to you if you'll shortly have access to a 'proper' piano. But for those without the necessary room or cash, this method might prove to be a viable alternative?
Good luck!
