Check out
Cisco IP Telephony: Planning, Design, Implementation, Operation, and Optimization
by Ramesh Kaza, Salman Asadullah
Publisher: Cisco Press
Pub Date: February 23, 2005
Print ISBN-10: 1-58705-157-5
Print ISBN-13: 978-1-58705-157-9
http://safari.ciscopress.com/1587051575
In CCO you may want to look
www.cisco.com/go/srnd
and Cisco Unity Design guide