The location of JavaPhone.jar should be added to the classpath variable for running Java applications which use JavaPhone APIs.This can be done by editing the classpath variable in the autoexec.bat (Windows 98) or in Control Panel -> System -> Environment (Windows NT).
For example in Windows 98 the classpath variable could be as follows:
where the c:\jdk1.1.8\lib\classes\ folder contains Symbian classes and JavaPhone classes.
More information about classpath issues with the emulator and the device can be found in the SDK documentation:
Crystal V6 Edition for Java -> Java Developer's Guide for Crystal -> Java Development -> The default classpath.