On Adobe's website, I've found the answer:
Debugging the application on the
iPhone To debug the application on the
iPhone:
Compile the application with debug
support: In Flash Professional CS5,
compile using the “Quick publishing
for device debugging” setting. (See
Creating an iPhone application
installer file using the Packager for
iPhone included with in Flash
Professional CS5.) Using the PFI
command-line application, compile the
application with the target ipa-debug
option. (See Creating an iPhone
application installer file from the
command line.) Install the application
on the iPhone. On the iPhone, turn
Wi-Fi on and connect to the same
network as that of the development
computer. Start a debug session on
your development computer. In Flash
Professional CS5, choose Debug > Begin
Remote Debug Session > ActionScript
3.0. Run the application on the iPhone. The debug version of the
application will prompt you for the IP
address of the developer computer.
Enter the IP address and tap the OK
button. To obtain the IP address of
the development computer. On Mac OS,
on the Apple menu, choose System
Preference. In the System Preferences
window, click the Network icon. The
Network preferences window lists the
IP address. On Windows, start a
command-line session and run the
ipconfig command.