It is required to build an app for iOS, Android & Blackberry with paid subscription, every stock market will have a different price.
So the app will need to show delayed feed for non-subscribers & live ones for subscribers.
Also the app will need to deliver alert to subscribers of each market respectively with buy/sell signals.
Users should be able to build their portfolios in their account to see the performance of their stocks.
A payment method needs to be integrated to pay for the subscription from within the app.