Boy you're aiming high here ;-}
First the iPhone won't do it. You need a Unix based system that will allow you to do parallel processing if you want a Cray type of system.
If you want something to track the trades you may want to build a home base system which you can access via your iPhone. That way you can have a big powerful system as your back end.
As to trading on the stock market. You do know the big traders have very large systems which are very close to the trading floor so their bids only take milliseconds or less using automated systems to do the bidding, buying and selling based on what the market trends are.