lmirak provided insightful info about device communication(especially about GameKit). I would like to add one more solution. You can use WiFi network to do your device communication.
See the link or download the sample application from developer.apple
The sample application named as WiTap. It demonstrates how to achieve network communication between applications. Using Bonjour, the application both advertises itself on the local network and displays a list of other instances of this application on the network.