That book is a bit old, but it is a good resource to start with. You can find that book on O'Reilly Network Safari, which has a free 2-week trial (you can read the book online!):
http://safari.oreilly.com/
That book is based on an older version of the IP Phone SDK, but still has good information on getting started. You can get a more current version of the SDK from Cisco (see below)...
For more information, this link provides more information on the XML tags available for the IP Phones:
http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_administration_guide_book09186a00801e8bc0.html
For more complete information, you may want to get the IP Phone SDK, available from Cisco's Developer Support program. The SDK provides more information on developing applications for the IP Phones, and has example applications in both ASP and JSP.
This page describes the IP Phone SDK:
http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_programming_reference_guide_chapter09186a00801fb6dc.html
This page describes the Cisco Developer Support Program:
http://www.cisco.com/pcgi-bin/dev_support/access_level/product_support
