I got the way to do it. But I wonder whether is a best practice or not.
Download the RPC jar lib:
ws-xmlrpc - Apache XML-RPC
Take the binary package.
Since your Zimlet is consuming (client), copy these .jar file to your Zimlet's directory:
- xmlrpc-client-3.1.x.jar
- xmlrpc-common-3.1.x.jar
- ws-commons-util-1.0.x.jar
You have to place this files under /opt/zimbra/jetty/service/WEB-INF/lib and restart your mailbox services in order to see the effects. If you are using zimbra desktop, it will be more easy and will not affect your live server. 
Write a jsp script file which import the following package:
Code:
<%@ page language="java" import="org.apache.xmlrpc.client.XmlRpcClient, org.apache.xmlrpc.client.XmlRpcClientConfigImpl, java.net.URL" %>
XmlRpcClientConfigImpl cfg = new XmlRpcClientConfigImpl();
cfg.setServerURL(new URL("http://localhost/xmlrpc-server.php/services"));
XmlRpcClient client = new XmlRpcClient();
client.setConfig(cfg);
Object[] parameters = new Object[] {"param1", "param2"};
// Beware of the return type. Type cast it accordingly. See the documentation at:
// http://ws.apache.org/xmlrpc/
Object returned_value = (Object) client.execute("method_name", parameters); So far I got it working. The documentation in: ws-xmlrpc - Apache XML-RPC is not completely correct. You have to debug your own sometimes.
Hope this help.