I found this book very helpful, descriptive and a very good introduction to SIP and it's services.

This book gives good insight into the commercial and business aspects of SIP usage, but this is not a technical book on SIP. Also some of the claims the author makes on penetration of SIP in the industry are debatable. Carrier Grade VoIP by Danial Collins is more useful technical book(despite being a non SIP centric book).

Very interesting approach to SIP had a lot of good information about what the future may bring

I bought this book to better understand the inner workings of SIP but, instead, was greeted with a superficial introduction to a miriad of SIP applications, services and options. At the end of the day RFC3261 is a much better source of information, as dry as it might be. As such, I cannot recommend this book to anyone trying to learn the intricacies of SIP.

This books presents SIP, the protocol for Session Initiation. It covers many aspects, including conferencing, security, Internet telephony, user preferences.

The book is not 400+ pages as Amazon indicates but just below 300. Why does this matter? Because, with 17 chapters, this gives an average of less than 20 pages per chapter. As you can guess, 20 pages are not sufficient to explain topics such as Internet telephony, or conferencing. Even the SIP protocol is not presented fully. Only the major messages are listed with a short description of their use.

I was also disappointed by the book organization. The SIP Overview chapter which explains how SIP works is chapter 5. All the preceeding chapters mention SIP before we even know what SIP is. This is most confusing unless you have already some SIP knowledge.

The book tries to cover too much. We get a whirlwind tour of many topics, none of them explained appropriately. The book opens many issues that remain unanswered. If you want a shallow overview of SIP, this book may meet your need. But you are likely to quickly need something more in-depth.