MIDPLogger and on device debugging
No all the MIDP phones support on-device debugging. All Java phones from Motorola iDEN support debugging on actual devices through HyperTerminal. Sony Ericsson T610 supports debugging through a bluetooth connection. For other phones that do not support on-device debugging directly, you may write your own logging utility or try MIDPLogger:
"To help debug issues that exist when running a MIDlet on device, MIDPLogger provides an on-device log file, log writer and log viewer capability. By integrating the MIDPLogger class within your MIDLet, you can write debug/trace information to an on-device database (and also to the console if you like, for when you are running in your emulator). You can browse and otherwise manage the on-device log file using the MIDPLogViewer MIDlet, by adding it to your MIDlet suite."
Other platforms:
BREW: You can connect your phone using a USB cable and use the BREW logger utility.
Symbian: Check this article on NewLC: On Target debugging with Series 60 devices.
