If you're genuinely interested in becoming proficient in building Call Handlers, chaining them & doing other nifty things with them, I can heartily recommend David Schultz's book entitled "CISCO UNITY CONNECTION" available from Cisco Press. It may also be available electronically in .pdf format. Personally I prefer hardcopy. Approx. 550 pages total. Clear, concise & fairly easy to follow (which alone says a lot, as most Cisco docs are very dry reading).
First printing: June 2011
Published by Cisco Press
800 East 96th Street
Indianapolis, IN 46240
The book takes you completely through the Cisco Unity Connection voice mail system.
By many accounts, it is "The Bible" of Unity Connection.
Original MUG/NAMU Charter Member