You have to provide your own XML for the phone idle screen.
You specify a link at the device level under the field 'idle'. Cisco provides a downloadable SDK with examples in both ASP and JSP of IP phone services. Some of these may be usable to you as idle screens. The clock.asp service is very popular with my users.
Note that you will need to provide a web server to host these files. In the 'idle' field, you would enter the URL to reach the particular service you want.