If you're looking to learn about mobile marketing - I highly recommend buying this book, it provides a great introduction to mobile marketing. And where Kim can't get in depth on certain topics, she provides resources that you can utilize to get more information.
She provides great information on how to determine if your target demographic aligns well with the mobile crowd and whether or not it is worth pursuing. She provides great demographic hints related to both culture and age that I wasn't aware of.
Also, she effectively presents all the different players that need to come into play for a successful mobile marketing campaign - like short code providers, aggregators, text message companies and more. You can't just start a mobile campaign without having your ducks in a row, and Kim tells you what you need to consider before starting. Although I have created mobile websites in the past, I hadn't considered all of these factors when it came to effectively marketing a mobile website.
The only reason I'm giving this boof 4 stars instead of 5 is because I thought it was a bit light on content in some areas - especially related to mobile search. Since this is the area that most interests me I would have liked more insight about pay-per-call, click-to-call, and examples of campaigns that actually had success. I would have liked to have seen screenshots of AdWords for setting up a mobile campaign and how ads look on a mobile browser. I would have liked to have seen the Google mobile search interface - and I am curious why Google mobile search defaults to web results instead of mobile (at least for me). But I do realize that I'm being a bit nitpicky and that in order to do all of this for each content area would have resulted in a 2000 page book.
Overall, if you're interested in mobile marketing, I highly recommend this book. While it can't get into the depth I would like in certain areas, it provides a fantastic jumping off point as well as links to plenty of resources to get the answers that you need.