A: 

The easiest way to check your usage is to run the app on a device and just reset the counters. Before launching the device, go to Settings -> General -> Usage and tap on the "Reset Statistics" button. Now all of the counters will reset to zero.

Next go to Settings -> Wi-Fi and ensure that your Wi-Fi is turned off. Now you will get all of your data over the Cellular Network and there are counters for the data on the Usage screen.

Now run your application. After you have done things you can go back to Settings -> General -> Usage and you will have data for how much data was sent and received.

Because iPhone OS4 supports multitasking, be sure that your application is the only application running during the test.

Walter