Some time ago, I mentioned 2 eBooks that were available freely from Realtime Publishers. Meanwhile 2 more interesting eBooks have been released: 

• The Essentials Series: Messaging and Web Security, by Dan Sullivan, continues the series’ focus on managing IT infrastructure and applications in an increasingly complex security environment. The articles are especially geared towards application developers, database administrators, Web architects, and systems managers, and focus on emerging threats to enterprise as well as SMB environments.
• The Definitive Guide to Successful Deployment of VoIP and IP Telephony, by IP Telephony expert Jim Cavanagh, provides practical insights into the specific steps organizations need to take to be successful with the implementation of VoIP and Internet Protocol Telephony. This book goes beyond the theoretical and provides insights and guidance gleaned from work with some of the largest enterprises, institutions, and agencies around the world. It puts that knowledge into a form that can be put right to work. Written in a clear, concise format for both technical and non-technical professionals alike, this book provides checklists and electronic “Report Cards” that implementers can use to select and deploy the right telephony solutions, applications, services, and testing and monitoring tools for their own specific situations.