On ClickZ, Laura Marriott tries to find out whether North America is ahead or behind Europe when it comes to mobile marketing. It a quite interesting article to realize the differences among the two continents, and understand the solutions (not the strategies!) which can perform better.
For example, in the US mobile search, mobile advertising, and mobile video initiatives are very popular, while text-based campaigns deliver the best results in Europe.
If you're interested in the topic, you can also download a recent case study by the Mobile Marketing Association. Also, on Mobhappy, Carlo Longino has recently posted a good analysis of the importance of (mobile advertising) to support and therefore deliver free content.