[ho_ming_tat],
See my other reply to a thread that asked for similar features:
http://forum.java.sun.com/thread.jsp?forum=50&thread=181344
In addition to what I have said in that thread, the System.getproperty() and the MIDlet.getAppProperty() methods do not return any values for identifying the unique information for the devices e.g. phone number or handset id. Implementations of such system properties must be provided by the device manufacturer itself and it can vary from one device to another. CLDC/MIDP does not provide a library function that extracts unique device information AFAIK.
HTH.
Allen Lai
Developer Technical Support
SUN Microsystems
http://www.sun.com/developers/support/