To exchange data using the iPhone SDK, you must use the GameKit Framework .
You can see this sample code or this code sample from a live application in the app store or the code mentioned by Randolph, here .
The main process is setting up the controller and delegate to work with the Bluetooth connection for you. Your delegate should handle things like "Connected to a peer-to-peer network" or "Received data."
In addition, you should note that the simulator does not work with Bluetooth, so you need two real iOS devices or more for testing.