There is a slight change between how one can pause an application in S60 phones and in JP phones. Here is how you can do it
Set Jad property Nokia-MIDlet-Background-Event: pause .

Listen to event hideNotify().
Upon reception call your pauseApp. Most developers tend call pauseApp() manually.

More on Java applications at http://developer.sonyericsson.com/site/global/docstools/java/p_java.jsp