*) Download your app to the iPhone as usual, you want a release build for performance testing
*) Launch the app on the device
*) Launch /Developer/Applications/Performance Tools/Shark in the Finder
*) Choose Sampling>Network/iPhone menu item
*) Choose your device in the window
*) Choose the application from the popup menu under Target so only your app is sampled
*) Click Start button in window
*) Do stuff in test application
*) Click Stop in window