Cisco Press has a book on how to do this. Here’s it’s ISBN number: 1-58705-060-9.
It’s pretty easy to understand.
Also Cisco’s CTE-1450 device allows you to port standard HTML to an IP Phone.
http://www.cisco.com/en/US/products/hw/contnetw/ps797/index.html
Also This product is good at making logos for the phones in addition to providing a bulletin board type of service for the phones.