Some Good books on VoIP

Switching to VoIP by Theodore Wallingford	Voice over IP Fundamentals by Jonathan Davidson, James Peters, and Brian Gracely	VoIP For Dummies (For Dummies (Computer/Tech)) by Timothy V. Kelly
VoIP Hacks: Tips & Tools for Internet Telephony (Hacks) by Ted Wallingford	Practical VoIP Security by Thomas Porter and Jan Kanclirz Jr.	SIP Beyond VoIP: The Next Step in the IP Communications Revolution by Henry Sinnreich, Alan B. Johnston, Robert J. Sparks, and Vinton G. Cerf
Taking Charge of Your VoIP Project by John Q. Walker and Jeffrey T. Hicks	Building a Voip Network with Nortel's Multimedia Communication Server 5100 by Larry Chafflin and Larry Chaffin	Softswitch : Architecture for VoIP (Professional Telecom) by Frank Ohrtman