The book is dense with the acronym-ridden jargon of this field. To someone new to the Internet Protocol, this can be a practical impediment to understanding. What you have to do is grit your teeth and focus on the ideas beneath the terminology.
The subject itself is potentially quite promising. One possible direction for richer multimedia messages, in the limit of "convergence". The book also addresses mostly the prospect of wireless messaging, ie. cellphones. While IMS can certainly occur on the traditional landline connections to the Internet, it is the tie-ins to mobile networks that motivates much of the text.