I wouldn't advise using the flashcard book a primary study source. For once, CVOICE is just one of the three sections in the book (the other two being for the QoS and CIPT exams). In addition to the flash cards for CVOICE, there are approximately 40 pages of review material for the exam. Together, it all makes for a great supplemental study guide to fill in any holes, as well as help you find ones you didn't know existed. Another plus is the CD with practice exam questions for all three exams.
I used the Cisco Voice over Frame Relay, ATM, and IP from Cisco Press as my primary study book. There is a lot more detail (i.e. command sets, hardware profiles) that isn't really necessary for the exam, but it provides an excellent foundation which the flash card book compliments very well.
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Cisco IP Telephony Flash Cards and Exam Practice Pack
I've send them an email asking if they are going to release a guide for the 642-432 CVOICE exam, I'll post their reply here.
I used the Cisco Voice over Frame Relay, ATM, and IP from Cisco Press as my primary study book. There is a lot more detail (i.e. command sets, hardware profiles) that isn't really necessary for the exam, but it provides an excellent foundation which the flash card book compliments very well.